kicad/gerbview/json11.cpp

/* Copyright (c) 2013 Dropbox, Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "json11.hpp"
#include <cassert>
#include <cmath>
#include <cstdlib>
#include <cstdio>
#include <limits>

namespace json11 {
static const int max_depth = 200;

using std::string;
using std::vector;
using std::map;
using std::make_shared;
using std::initializer_list;
using std::move;

/* Helper for representing null - just a do-nothing struct, plus comparison
 * operators so the helpers in JsonValue work. We can't use nullptr_t because
 * it may not be orderable.
 */
struct NullStruct
{
    bool operator==( NullStruct ) const { return true; }
    bool operator<( NullStruct ) const { return false; }
};

/* * * * * * * * * * * * * * * * * * * *
 * Serialization
 */

static void indent( int level, string& out )
{
    for( int i = 0; i < level * 2; i++ )
        out += " ";
}


static void dump( NullStruct, int level, string& out )
{
    out += "null";
}


static void dump( double value, int level, string& out )
{
    indent( level, out );

    if( std::isfinite( value ) )
    {
        char buf[32];
        snprintf( buf, sizeof buf, "%.3f", value );
        out += buf;
    }
    else
    {
        out += "null";
    }
}


static void dump( int value, int level, string& out )
{
    indent( level, out );

    char buf[32];

    snprintf( buf, sizeof buf, "%d", value );
    out += buf;
}


static void dump( bool value, int level, string& out )
{
    indent( level, out );

    out += value ? "true" : "false";
}


static void dump( const string& value, int level, string& out )
{
    indent( level, out );

    out += '"';

    for( size_t i = 0; i < value.length(); i++ )
    {
        const char ch = value[i];

        if( ch == '\\' )
        {
            out += "\\\\";
        }
        else if( ch == '"' )
        {
            out += "\\\"";
        }
        else if( ch == '\b' )
        {
            out += "\\b";
        }
        else if( ch == '\f' )
        {
            out += "\\f";
        }
        else if( ch == '\n' )
        {
            out += "\\n";
        }
        else if( ch == '\r' )
        {
            out += "\\r";
        }
        else if( ch == '\t' )
        {
            out += "\\t";
        }
        else if( static_cast<uint8_t>(ch) <= 0x1f )
        {
            char buf[8];
            snprintf( buf, sizeof buf, "\\u%04x", ch );
            out += buf;
        }
        else if( static_cast<uint8_t>(ch) == 0xe2 && static_cast<uint8_t>(value[i + 1]) == 0x80
                 && static_cast<uint8_t>(value[i + 2]) == 0xa8 )
        {
            out += "\\u2028";
            i += 2;
        }
        else if( static_cast<uint8_t>(ch) == 0xe2 && static_cast<uint8_t>(value[i + 1]) == 0x80
                 && static_cast<uint8_t>(value[i + 2]) == 0xa9 )
        {
            out += "\\u2029";
            i += 2;
        }
        else
        {
            out += ch;
        }
    }

    out += '"';
}


static void dump( const Json::array& values, int level, string& out )
{
    bool first = true;

    indent( level, out );
    out += "[\n";

    for( const auto& value : values )
    {
        if( !first )
            out += ",\n";

        value.dump( level + 1, out );
        first = false;
    }

    out += "\n";
    indent( level, out );
    out += "]";
}


static void dump( const Json::object& values, int level, string& out )
{
    bool first = true;

    indent( level, out );
    out += "{\n";

    for( int i : { 1, 2 } )
    {
        for( const auto& kv : values )
        {
            if( i == 1 && kv.first != "Header" )
                continue;
            else if( i == 2 && kv.first == "Header" )
                continue;

            if( !first )
                out += ",\n";

            dump( kv.first, level + 1, out );
            out += ": ";
            if( kv.second.is_object() || kv.second.is_array() )
            {
                out += "\n";
                kv.second.dump( level + 1, out );
            }
            else
            {
                kv.second.dump( 1, out );
            }
            first = false;
        }
    }

    out += "\n";
    indent( level, out );
    out += "}";
}


void Json::dump( int level, string& out ) const
{
    m_ptr->dump( level, out );
}


/* * * * * * * * * * * * * * * * * * * *
 * Value wrappers
 */

template <Json::Type tag, typename T>
class Value : public JsonValue
{
protected:

    // Constructors
    explicit Value( const T& value ) : m_value( value ) {}
    explicit Value( T&& value )      : m_value( move( value ) ) {}

    // Get type tag
    Json::Type type() const override
    {
        return tag;
    }

    // Comparisons
    bool equals( const JsonValue* other ) const override
    {
        return m_value == static_cast<const Value<tag, T>*>(other)->m_value;
    }

    bool less( const JsonValue* other ) const override
    {
        return m_value < static_cast<const Value<tag, T>*>(other)->m_value;
    }

    T m_value;
    void dump( int level, string& out ) const override { json11::dump( m_value, level, out ); }
};

class JsonDouble final : public Value<Json::NUMBER, double>
{
    double number_value() const override { return m_value; }
    int int_value() const override { return static_cast<int>(m_value); }
    bool equals( const JsonValue* other ) const override
    {
        return m_value == other->number_value();
    }
    bool less( const JsonValue* other )   const override
    {
        return m_value <  other->number_value();
    }

public:
    explicit JsonDouble( double value ) : Value( value ) {}
};

class JsonInt final : public Value<Json::NUMBER, int>
{
    double number_value() const override { return m_value; }
    int int_value() const override { return m_value; }
    bool equals( const JsonValue* other ) const override
    {
        return m_value == other->number_value();
    }
    bool less( const JsonValue* other )   const override
    {
        return m_value <  other->number_value();
    }

public:
    explicit JsonInt( int value ) : Value( value ) {}
};

class JsonBoolean final : public Value<Json::BOOL, bool>
{
    bool bool_value() const override { return m_value; }

public:
    explicit JsonBoolean( bool value ) : Value( value ) {}
};

class JsonString final : public Value<Json::STRING, string>
{
    const string& string_value() const override { return m_value; }

    void set_string_value( string value ) const override
    {
        const_cast<JsonString*>( this )->m_value = value;
    }

public:
    explicit JsonString( const string& value ) : Value( value ) {}
    explicit JsonString( string&& value )      : Value( move( value ) ) {}
};

class JsonArray final : public Value<Json::ARRAY, Json::array>
{
    const Json::array& array_items() const override { return m_value; }
    const Json& operator[]( size_t i ) const override;

public:
    explicit JsonArray( const Json::array& value ) : Value( value ) {}
    explicit JsonArray( Json::array&& value )      : Value( move( value ) ) {}
};

class JsonObject final : public Value<Json::OBJECT, Json::object>
{
    const Json::object& object_items() const override { return m_value; }
    const Json& operator[]( const string& key ) const override;

public:
    explicit JsonObject( const Json::object& value ) : Value( value ) {}
    explicit JsonObject( Json::object&& value )      : Value( move( value ) ) {}
};

class JsonNull final : public Value<Json::NUL, NullStruct>
{
public:
    JsonNull() : Value( {} ) {}
};

/* * * * * * * * * * * * * * * * * * * *
 * Static globals - static-init-safe
 */
struct Statics
{
    const std::shared_ptr<JsonValue> null   = make_shared<JsonNull>();
    const std::shared_ptr<JsonValue> t  = make_shared<JsonBoolean>( true );
    const std::shared_ptr<JsonValue> f  = make_shared<JsonBoolean>( false );
    const string empty_string;
    const vector<Json> empty_vector;
    const map<string, Json> empty_map;
    Statics() {}
};

static const Statics& statics()
{
    static const Statics s {};

    return s;
}


static const Json& static_null()
{
    // This has to be separate, not in Statics, because Json() accesses statics().null.
    static const Json json_null;

    return json_null;
}


/* * * * * * * * * * * * * * * * * * * *
 * Constructors
 */

Json::Json() noexcept                  : m_ptr( statics().null )
{
}


Json::Json( std::nullptr_t ) noexcept    : m_ptr( statics().null )
{
}


Json::Json( double value )               : m_ptr( make_shared<JsonDouble>( value ) )
{
}


Json::Json( int value )                  : m_ptr( make_shared<JsonInt>( value ) )
{
}


Json::Json( bool value )                 : m_ptr( value ? statics().t : statics().f )
{
}


Json::Json( const string& value )        : m_ptr( make_shared<JsonString>( value ) )
{
}


Json::Json( string&& value )             : m_ptr( make_shared<JsonString>( move( value ) ) )
{
}


Json::Json( const char* value )         : m_ptr( make_shared<JsonString>( value ) )
{
}


Json::Json( const Json::array& values )  : m_ptr( make_shared<JsonArray>( values ) )
{
}


Json::Json( Json::array&& values )       : m_ptr( make_shared<JsonArray>( move( values ) ) )
{
}


Json::Json( const Json::object& values ) : m_ptr( make_shared<JsonObject>( values ) )
{
}


Json::Json( Json::object&& values )      : m_ptr( make_shared<JsonObject>( move( values ) ) )
{
}


/* * * * * * * * * * * * * * * * * * * *
 * Accessors
 */

Json::Type Json::type()                           const
{
    return m_ptr->type();
}


double Json::number_value()                       const
{
    return m_ptr->number_value();
}


int Json::int_value()                             const
{
    return m_ptr->int_value();
}


bool Json::bool_value()                           const
{
    return m_ptr->bool_value();
}


const string& Json::string_value()               const
{
    return m_ptr->string_value();
}


void Json::set_string_value( string value ) const
{
    m_ptr->set_string_value( value );
}


const vector<Json>& Json::array_items()          const
{
    return m_ptr->array_items();
}


const map<string, Json>& Json::object_items()    const
{
    return m_ptr->object_items();
}


const Json& Json::operator[]( size_t i )          const
{
    return (*m_ptr)[i];
}


const Json& Json::operator[]( const string& key ) const
{
    return (*m_ptr)[key];
}


double JsonValue::number_value()              const
{
    return 0;
}


int JsonValue::int_value()                 const
{
    return 0;
}


bool JsonValue::bool_value()                const
{
    return false;
}


const string& JsonValue::string_value()              const
{
    return statics().empty_string;
}

void JsonValue::set_string_value( string value ) const
{
}


const vector<Json>& JsonValue::array_items()               const
{
    return statics().empty_vector;
}


const map<string, Json>& JsonValue::object_items()              const
{
    return statics().empty_map;
}


const Json& JsonValue::operator[]( size_t )         const
{
    return static_null();
}


const Json& JsonValue::operator[]( const string& ) const
{
    return static_null();
}


const Json& JsonObject::operator[]( const string& key ) const
{
    auto iter = m_value.find( key );

    return ( iter == m_value.end() ) ? static_null() : iter->second;
}


const Json& JsonArray::operator[]( size_t i ) const
{
    if( i >= m_value.size() )
        return static_null();
    else
        return m_value[i];
}


/* * * * * * * * * * * * * * * * * * * *
 * Comparison
 */

bool Json::operator==( const Json& other ) const
{
    if( m_ptr == other.m_ptr )
        return true;

    if( m_ptr->type() != other.m_ptr->type() )
        return false;

    return m_ptr->equals( other.m_ptr.get() );
}


bool Json::operator<( const Json& other ) const
{
    if( m_ptr == other.m_ptr )
        return false;

    if( m_ptr->type() != other.m_ptr->type() )
        return m_ptr->type() < other.m_ptr->type();

    return m_ptr->less( other.m_ptr.get() );
}


/* * * * * * * * * * * * * * * * * * * *
 * Parsing
 */

/* esc(c)
 *
 * Format char c suitable for printing in an error message.
 */
static inline string esc( char c )
{
    char buf[12];

    if( static_cast<uint8_t>(c) >= 0x20 && static_cast<uint8_t>(c) <= 0x7f )
    {
        snprintf( buf, sizeof buf, "'%c' (%d)", c, c );
    }
    else
    {
        snprintf( buf, sizeof buf, "(%d)", c );
    }

    return string( buf );
}


static inline bool in_range( long x, long lower, long upper )
{
    return x >= lower && x <= upper;
}


namespace {
/* JsonParser
 *
 * Object that tracks all state of an in-progress parse.
 */
struct JsonParser final
{
    /* State
     */
    const string& str;
    size_t i;
    string& err;
    bool failed;
    const JsonParse strategy;

    /* fail(msg, err_ret = Json())
     *
     * Mark this parse as failed.
     */
    Json fail( string&& msg )
    {
        return fail( move( msg ), Json() );
    }

    template <typename T>
    T fail( string&& msg, const T err_ret )
    {
        if( !failed )
            err = std::move( msg );

        failed = true;
        return err_ret;
    }

    /* consume_whitespace()
     *
     * Advance until the current character is non-whitespace.
     */
    void consume_whitespace()
    {
        while( str[i] == ' ' || str[i] == '\r' || str[i] == '\n' || str[i] == '\t' )
            i++;
    }

    /* consume_comment()
     *
     * Advance comments (c-style inline and multiline).
     */
    bool consume_comment()
    {
        bool comment_found = false;

        if( str[i] == '/' )
        {
            i++;

            if( i == str.size() )
                return fail( "unexpected end of input after start of comment", false );

            if( str[i] == '/' ) // inline comment
            {
                i++;

                // advance until next line, or end of input
                while( i < str.size() && str[i] != '\n' )
                {
                    i++;
                }

                comment_found = true;
            }
            else if( str[i] == '*' ) // multiline comment
            {
                i++;

                if( i > str.size() - 2 )
                    return fail( "unexpected end of input inside multi-line comment", false );

                // advance until closing tokens
                while( !(str[i] == '*' && str[i + 1] == '/') )
                {
                    i++;

                    if( i > str.size() - 2 )
                        return fail(
                                "unexpected end of input inside multi-line comment", false );
                }

                i += 2;
                comment_found = true;
            }
            else
                return fail( "malformed comment", false );
        }

        return comment_found;
    }

    /* consume_garbage()
     *
     * Advance until the current character is non-whitespace and non-comment.
     */
    void consume_garbage()
    {
        consume_whitespace();

        if( strategy == JsonParse::COMMENTS )
        {
            bool comment_found = false;

            do {
                comment_found = consume_comment();

                if( failed ) return;

                consume_whitespace();
            } while( comment_found );
        }
    }

    /* get_next_token()
     *
     * Return the next non-whitespace character. If the end of the input is reached,
     * flag an error and return 0.
     */
    char get_next_token()
    {
        consume_garbage();

        if( failed ) return (char) 0;

        if( i == str.size() )
            return fail( "unexpected end of input", (char) 0 );

        return str[i++];
    }

    /* encode_utf8(pt, out)
     *
     * Encode pt as UTF-8 and add it to out.
     */
    void encode_utf8( long pt, string& out )
    {
        if( pt < 0 )
            return;

        if( pt < 0x80 )
        {
            out += static_cast<char>(pt);
        }
        else if( pt < 0x800 )
        {
            out += static_cast<char>( (pt >> 6) | 0xC0 );
            out += static_cast<char>( (pt & 0x3F) | 0x80 );
        }
        else if( pt < 0x10000 )
        {
            out += static_cast<char>( (pt >> 12) | 0xE0 );
            out += static_cast<char>( ( (pt >> 6) & 0x3F ) | 0x80 );
            out += static_cast<char>( (pt & 0x3F) | 0x80 );
        }
        else
        {
            out += static_cast<char>( (pt >> 18) | 0xF0 );
            out += static_cast<char>( ( (pt >> 12) & 0x3F ) | 0x80 );
            out += static_cast<char>( ( (pt >> 6) & 0x3F ) | 0x80 );
            out += static_cast<char>( (pt & 0x3F) | 0x80 );
        }
    }

    /* parse_string()
     *
     * Parse a string, starting at the current position.
     */
    string parse_string()
    {
        string out;
        long last_escaped_codepoint = -1;

        while( true )
        {
            if( i == str.size() )
                return fail( "unexpected end of input in string", "" );

            char ch = str[i++];

            if( ch == '"' )
            {
                encode_utf8( last_escaped_codepoint, out );
                return out;
            }

            if( in_range( ch, 0, 0x1f ) )
                return fail( "unescaped " + esc( ch ) + " in string", "" );

            // The usual case: non-escaped characters
            if( ch != '\\' )
            {
                encode_utf8( last_escaped_codepoint, out );
                last_escaped_codepoint = -1;
                out += ch;
                continue;
            }

            // Handle escapes
            if( i == str.size() )
                return fail( "unexpected end of input in string", "" );

            ch = str[i++];

            if( ch == 'u' )
            {
                // Extract 4-byte escape sequence
                string esc = str.substr( i, 4 );

                // Explicitly check length of the substring. The following loop
                // relies on std::string returning the terminating NUL when
                // accessing str[length]. Checking here reduces brittleness.
                if( esc.length() < 4 )
                {
                    return fail( "bad \\u escape: " + esc, "" );
                }

                for( size_t j = 0; j < 4; j++ )
                {
                    if( !in_range( esc[j], 'a', 'f' ) && !in_range( esc[j], 'A', 'F' )
                        && !in_range( esc[j], '0', '9' ) )
                        return fail( "bad \\u escape: " + esc, "" );
                }

                long codepoint = strtol( esc.data(), nullptr, 16 );

                // JSON specifies that characters outside the BMP shall be encoded as a pair
                // of 4-hex-digit \u escapes encoding their surrogate pair components. Check
                // whether we're in the middle of such a beast: the previous codepoint was an
                // escaped lead (high) surrogate, and this is a trail (low) surrogate.
                if( in_range( last_escaped_codepoint, 0xD800, 0xDBFF )
                    && in_range( codepoint, 0xDC00, 0xDFFF ) )
                {
                    // Reassemble the two surrogate pairs into one astral-plane character, per
                    // the UTF-16 algorithm.
                    encode_utf8( ( ( (last_escaped_codepoint - 0xD800) << 10 )
                                   | (codepoint - 0xDC00) ) + 0x10000, out );
                    last_escaped_codepoint = -1;
                }
                else
                {
                    encode_utf8( last_escaped_codepoint, out );
                    last_escaped_codepoint = codepoint;
                }

                i += 4;
                continue;
            }

            encode_utf8( last_escaped_codepoint, out );
            last_escaped_codepoint = -1;

            if( ch == 'b' )
            {
                out += '\b';
            }
            else if( ch == 'f' )
            {
                out += '\f';
            }
            else if( ch == 'n' )
            {
                out += '\n';
            }
            else if( ch == 'r' )
            {
                out += '\r';
            }
            else if( ch == 't' )
            {
                out += '\t';
            }
            else if( ch == '"' || ch == '\\' || ch == '/' )
            {
                out += ch;
            }
            else
            {
                return fail( "invalid escape character " + esc( ch ), "" );
            }
        }
    }

    /* parse_number()
     *
     * Parse a double.
     */
    Json parse_number()
    {
        size_t start_pos = i;

        if( str[i] == '-' )
            i++;

        // Integer part
        if( str[i] == '0' )
        {
            i++;

            if( in_range( str[i], '0', '9' ) )
                return fail( "leading 0s not permitted in numbers" );
        }
        else if( in_range( str[i], '1', '9' ) )
        {
            i++;

            while( in_range( str[i], '0', '9' ) )
                i++;
        }
        else
        {
            return fail( "invalid " + esc( str[i] ) + " in number" );
        }

        if( str[i] != '.' && str[i] != 'e' && str[i] != 'E'
            && (i - start_pos) <= static_cast<size_t>(std::numeric_limits<int>::digits10) )
        {
            return std::atoi( str.c_str() + start_pos );
        }

        // Decimal part
        if( str[i] == '.' )
        {
            i++;

            if( !in_range( str[i], '0', '9' ) )
                return fail( "at least one digit required in fractional part" );

            while( in_range( str[i], '0', '9' ) )
                i++;
        }

        // Exponent part
        if( str[i] == 'e' || str[i] == 'E' )
        {
            i++;

            if( str[i] == '+' || str[i] == '-' )
                i++;

            if( !in_range( str[i], '0', '9' ) )
                return fail( "at least one digit required in exponent" );

            while( in_range( str[i], '0', '9' ) )
                i++;
        }

        return std::strtod( str.c_str() + start_pos, nullptr );
    }

    /* expect(str, res)
     *
     * Expect that 'str' starts at the character that was just read. If it does, advance
     * the input and return res. If not, flag an error.
     */
    Json expect( const string& expected, Json res )
    {
        assert( i != 0 );
        i--;

        if( str.compare( i, expected.length(), expected ) == 0 )
        {
            i += expected.length();
            return res;
        }
        else
        {
            return fail( "parse error: expected " + expected + ", got " +
                    str.substr( i, expected.length() ) );
        }
    }

    /* parse_json()
     *
     * Parse a JSON object.
     */
    Json parse_json( int depth )
    {
        if( depth > max_depth )
        {
            return fail( "exceeded maximum nesting depth" );
        }

        char ch = get_next_token();

        if( failed )
            return Json();

        if( ch == '-' || (ch >= '0' && ch <= '9') )
        {
            i--;
            return parse_number();
        }

        if( ch == 't' )
            return expect( "true", true );

        if( ch == 'f' )
            return expect( "false", false );

        if( ch == 'n' )
            return expect( "null", Json() );

        if( ch == '"' )
            return parse_string();

        if( ch == '{' )
        {
            map<string, Json> data;
            ch = get_next_token();

            if( ch == '}' )
                return data;

            while( 1 )
            {
                if( ch != '"' )
                    return fail( "expected '\"' in object, got " + esc( ch ) );

                string key = parse_string();

                if( failed )
                    return Json();

                ch = get_next_token();

                if( ch != ':' )
                    return fail( "expected ':' in object, got " + esc( ch ) );

                data[std::move( key )] = parse_json( depth + 1 );

                if( failed )
                    return Json();

                ch = get_next_token();

                if( ch == '}' )
                    break;

                if( ch != ',' )
                    return fail( "expected ',' in object, got " + esc( ch ) );

                ch = get_next_token();
            }

            return data;
        }

        if( ch == '[' )
        {
            vector<Json> data;
            ch = get_next_token();

            if( ch == ']' )
                return data;

            while( 1 )
            {
                i--;
                data.push_back( parse_json( depth + 1 ) );

                if( failed )
                    return Json();

                ch = get_next_token();

                if( ch == ']' )
                    break;

                if( ch != ',' )
                    return fail( "expected ',' in list, got " + esc( ch ) );

                ch = get_next_token();
                (void) ch;
            }

            return data;
        }

        return fail( "expected value, got " + esc( ch ) );
    }
};
}    // namespace {

Json Json::parse( const string& in, string& err, JsonParse strategy )
{
    JsonParser parser {
        in, 0, err, false, strategy
    };
    Json result = parser.parse_json( 0 );

    // Check for any trailing garbage
    parser.consume_garbage();

    if( parser.failed )
        return Json();

    if( parser.i != in.size() )
        return parser.fail( "unexpected trailing " + esc( in[parser.i] ) );

    return result;
}


// Documented in json11.hpp
vector<Json> Json::parse_multi( const string& in,
        std::string::size_type& parser_stop_pos,
        string& err,
        JsonParse strategy )
{
    JsonParser parser {
        in, 0, err, false, strategy
    };

    parser_stop_pos = 0;
    vector<Json> json_vec;

    while( parser.i != in.size() && !parser.failed )
    {
        json_vec.push_back( parser.parse_json( 0 ) );

        if( parser.failed )
            break;

        // Check for another object
        parser.consume_garbage();

        if( parser.failed )
            break;

        parser_stop_pos = parser.i;
    }

    return json_vec;
}


/* * * * * * * * * * * * * * * * * * * *
 * Shape-checking
 */

bool Json::has_shape( const shape& types, string& err ) const
{
    if( !is_object() )
    {
        err = "expected JSON object, got " + dump( 0 );
        return false;
    }

    for( auto& item : types )
    {
        if( (*this)[item.first].type() != item.second )
        {
            err = "bad type for " + item.first + " in " + dump( 0 );
            return false;
        }
    }

    return true;
}
}    // namespace json11