ddn.data.json5¶

JSON5 parsing and serialization support for the D programming language.

Overview¶

The ddn.data.json5 module provides comprehensive support for JSON5, a superset of JSON that aims to be easier for humans to write and maintain. It includes a full-featured parser and writer that maps JSON5 values to and from ddn.var.

JSON5 Features Supported¶

JSON5 extends standard JSON with several human-friendly features:

Feature	Description
Comments	Single-line (`//`) and block (`/* */`) comments
Trailing commas	Allowed in arrays and objects
Unquoted keys	Object keys can be unquoted if they are valid identifiers
Single-quoted strings	Strings can use `'single quotes'`
Multi-line strings	Line continuations with backslash
Hexadecimal numbers	`0xDEADBEEF` notation
Leading/trailing decimals	`.5` and `5.` are valid
Explicit plus sign	`+1.5` is valid
Special numbers	`NaN`, `Infinity`, `-Infinity`
UTF-8 BOM	Accepted at the beginning of input

Type Mapping¶

JSON5 values are mapped to ddn.var types as follows:

JSON5 Value	`var.Type`
`null`	`NULL`
`true`, `false`	`BOOL`
Integer (fits `long`)	`LONG`
Integer (fits `ulong`, non-negative)	`ULONG`
Floating point, `NaN`, `Infinity`	`DOUBLE`
String (single or double quoted)	`STRING`
Array	`ARRAY`
Object	`OBJECT`

Usage Examples¶

Parsing JSON5¶

import ddn.data.json5;
import ddn.var;

Json5Error err;
var v;

// Parse JSON5 with trailing commas and unquoted keys
if (parseJSON5(v, "{a: 1, b: 'hello',}", err)) {
    assert(v["a"].as!long == 1);
    assert(v["b"].as!string == "hello");
} else {
    // Handle parse error
    writeln("Error at line ", err.line, ": ", err.message);
}

Writing JSON5¶

import ddn.data.json5;
import ddn.var;

var data;
data["name"] = "example";
data["values"] = [1, 2, 3];
data["active"] = true;

// Compact JSON5 output
string json5 = toJSON5(data);
// Output: {active:true,name:'example',values:[1,2,3]}

// Strict JSON output
string json = toJSON(data);
// Output: {"active":true,"name":"example","values":[1,2,3]}

Pretty Printing¶

Json5WriteOptions opts;
opts.pretty = true;
opts.indentWidth = 2;

string pretty = toJSON5(data, opts);
/* Output:
{
  active: true,
  name: 'example',
  values: [
    1,
    2,
    3,
  ],
}
*/

Minifying JSON5¶

// Remove comments and whitespace
string compact = minify("{ a: 1, // comment\n b: 2, }");
assert(compact == "{a:1,b:2,}");

Writer Behavior¶

Strict JSON Mode¶

When using toJSON() or writeMode = JSON:

All keys are quoted with double quotes
Strings use double quotes with standard escaping
NaN and Infinity are emitted as null (not valid in JSON)
No trailing commas
No comments

JSON5 Mode¶

When using toJSON5() or writeMode = JSON5:

Keys are unquoted when they are valid identifiers
Strings prefer single quotes (fewer escapes needed)
NaN, Infinity, -Infinity are preserved
Trailing commas are added (configurable)

Error Handling¶

The parser provides detailed error information:

Json5Error err;
var v;
if (!parseJSON5(v, "{ invalid }", err)) {
    writefln("Parse error at %d:%d - %s", err.line, err.column, err.message);
}

Performance Features¶

Scratch buffers: Use Json5WriteScratch for reduced allocations in hot paths
Depth limits: Configurable maxDepth prevents stack overflow on deeply nested input
Fast-path parsing: Simple literals are parsed efficiently

// Reuse scratch buffers for multiple serializations
Json5WriteScratch scratch;
foreach (item; items) {
    string json = toJSON5(item, Json5WriteOptions.init, scratch);
    // process json...
}