# fast_json - High-Performance MQL5 JSON Library

> "If your JSON parser needs recursion, you're doing it wrong."

## Overview

**fast_json** is a production-grade, high-performance JSON library for MQL5, engineered for scenarios where **I/O throughput** and **memory efficiency** are paramount.

Unlike standard libraries that fragment the heap with thousands of small object allocations, **fast_json** employs a **tape-based zero-allocation memory model**. It parses JSON directly into a contiguous integer array (the "tape"), enabling it to process gigabytes of data with minimal overhead and zero garbage collection pressure.

## Key Features

- **🚀 Zero-Alloc Tape Architecture**: Parses the entire JSON into a single contiguous integer array. No objects are created during parsing. 
- **⚡ SWAR Acceleration**: Uses Simulated 64-bit SWAR (SIMD within a Register) to scan 8 bytes at a time for structural characters, significantly reducing branch misprediction.
- **🛡️ Stack-Safe Iterative Parser**: Implemented as a finite state machine. Zero recursion. Immune to stack overflow from deeply nested JSONs.
- **🔧 Handle-Based Navigation**: Data access via lightweight `CJsonNode` structs that point to the tape. Copying nodes is free.
- **💾 High-Throughput I/O**: Optimized for rapid Read/Write operations, making it ideal for LLM integration, REST API consumption, and large dataset processing.

## Performance

| Metric | fast_json | Standard Libs |
|--------|-----------|---------------|
| **Allocation Strategy** | 1 contiguous block (Tape) | N objects per node |
| **Recursion Depth** | Unlimited (Heap stack) | Limited (Call stack) |
| **Read/Write Speed** | **EXTREME** (300MB/s+ Est.) | LOW |
| **Memory Fragmentation**| Near Zero | High |

## Installation instructions

### OPTION A: Via KnitPkg (recommended)

#### Prerequisites

To use `json_fast` in your KnitPkg project, you will need:

1.  [**MetaTrader 5**](https://www.mql5.com/) installed.
2.  [**KnitPkg CLI**](https://knitpkg.dev): The KnitPkg package manager for MetaTrader. If you don't have it, you can install it by following the instructions in the [KnitPkg documentation](https://docs.knitpkg.dev/installation/).

#### Installing as a dependency

Execute the following command in your project directory:

```bash
kp add @14134597/fast_json
kp install
```

### OPTION B: Manual installation

Simply download the header file `knitpkg/include/14134597/fast_json/fast_json.mqh` into your MetaTrader Include/ directory or
put this header along with your other source mql files.

## Usage

### Parsing
```mql5
#include "../knitpkg/include/14134597/fast_json/fast_json.mqh"

CJson toolkit;
string json = "{\"price\": 1.2345, \"currency\": \"EURUSD\"}";

if (toolkit.Parse(json)) {
    // Zero-copy access
    double price = toolkit["price"].ToDouble();
    string curr  = toolkit["currency"].ToString();
    Print(curr, ": ", price);
} 
```

### Building & Serializing
```mql5
CJsonBuilder builder;
builder.Obj()
       .Key("signal").Val("buy")
       .Key("volume").Val(0.1)
       .EndObj();

string payload = builder.Build();
// Result: {"signal":"buy","volume":0.1}
```

## Why fast_json?

Because typical MQL5 libraries were designed for configuration files, not high-throughput data streams. **fast_json** bridges that gap.

## Running unit tests with KnitPkg

You can execute `kp get` to query the KnitPkg Registry for metadata and automatically download/build the latest stable version of `fast_api`.

Example (run from your MetaTrader *Data Folder* root):

```bash
cd "C:\Users\username\AppData\Roaming\MetaQuotes\Terminal\<TERMINAL_ID>"

kp get mql5 @14134597/fast_json
```

In Metatrader, refresh the Navigator and then run the unit test scripts under Scripts/fast_json/bin


## License

MIT.