mir-ion

Fast ION binary and JSON serialization for D. Zero-copy parsing, automatic struct serialization via mir-core reflection, BetterC compatible read path.

📖 Full API reference → mir-ion.libmir.org — every module and symbol of mir-ion, regenerated from current source.

mir-ion is a serialization library for D that targets both Amazon Ion (a superset of JSON with a binary format) and plain JSON. Its design priorities are: zero-copy parsing, compile-time auto-generated codecs via mir-core reflection, and @nogc compatibility on the read path.

GitHub: libmir/mir-ion · Last commit: November 2025

Install

dependency "mir-ion" version="~>2.0"
dependency "mir-core" version="~>1.0"

JSON serialization

Struct → JSON string

import mir.ion.ser.json : serializeJson;
import mir.ion.deser.json : deserializeJson;

struct Point {
    double x;
    double y;
    string label;
}

auto p = Point(1.5, 2.5, "origin");
string json = p.serializeJson;
// {"x":1.5,"y":2.5,"label":"origin"}

JSON string → struct

auto p2 = deserializeJson!Point(`{"x": 3.0, "y": 4.0, "label": "B"}`);
assert(p2.x == 3.0);

Nested structs and arrays

import mir.ndslice : slice;

struct Dataset {
    string name;
    double[] values;
}

auto ds = Dataset("test", [1.0, 2.0, 3.0]);
string json = ds.serializeJson;
// {"name":"test","values":[1.0,2.0,3.0]}

Custom serialization keys

import mir.ion.ser : serdeKeys, serdeIgnore;

struct Config {
    @serdeKeys("max_iter", "maxIter")
    int maxIterations = 100;

    @serdeIgnore
    string internalNote;
}

ION binary format

ION binary is more compact and faster to parse than JSON. Use it for internal data exchange:

import mir.ion.ser.ion : serializeIon;
import mir.ion.deser.ion : deserializeIon;

ubyte[] binary = p.serializeIon;
auto p3 = deserializeIon!Point(binary);

ION binary uses a type-annotated format — no quoting, no parsing of number strings.

Streaming / zero-copy parsing

For large inputs, parse without building an intermediate DOM:

import mir.ion.value : IonDescribedValue;
import mir.ion.stream : IonStream;

// Iterate over top-level ION values in a stream
foreach (IonDescribedValue v; IonStream(buffer)) {
    // process v without full deserialization
}

Comparison with std.json and asdf

Feature	`std.json`	`asdf`	`mir-ion`
Zero-copy	No	No	Yes
Binary ION	No	No	Yes
Auto struct codec	No	Yes	Yes
`@nogc` read	No	No	Yes
BetterC	No	No	Yes (read)
Custom keys	No	Yes	Yes

Relationship to mir-core

mir-ion uses mir.reflection (from mir-core) to introspect struct fields at compile time and generate serialization/deserialization code automatically. No macros or separate schema files needed.

Serialization (JSON / MessagePack / ION)

mir-ion

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