simple_json

High-Level JSON Parsing and Building for Eiffel

MIT License Eiffel 25.02 Design by Contract

Overview

simple_json is a production-ready JSON library for Eiffel that builds on the standard eJSON library to provide modern features. It offers JSON Schema validation (Draft 7), JSON Pointer navigation (RFC 6901), JSON Patch operations (RFC 6902), JSON Merge Patch (RFC 7386), JSONPath queries, and comprehensive error tracking.

Part of the Simple Eiffel ecosystem.

Quick Start

Installation

  1. Set the environment variable: 
    export SIMPLE_EIFFEL=/d/prod
  2. Add to your ECF file: 
    <library name="simple_json" location="$SIMPLE_EIFFEL/simple_json/simple_json.ecf"/>

Parse & Navigate

local
    json: SIMPLE_JSON
    value: SIMPLE_JSON_VALUE
do
    create json
    if attached json.parse ('{"users": [{"name": "Alice"}]}') as v then
        -- Use JSONPath query
        print (json.query_string (v, "$.users[0].name"))  -- "Alice"
    end
end

Build JSON

local
    obj: SIMPLE_JSON_OBJECT
do
    obj := json.new_object
        .put_string ("name", "Alice")
        .put_integer ("age", 30)
        .put_boolean ("active", True)

    print (obj.to_json)
    -- {"name":"Alice","age":30,"active":true}
end

Key Features

JSON Schema Validation

Draft 7 support - the only Eiffel library with JSON Schema validation.

JSON Pointer (RFC 6901)

Navigate JSON with simple path expressions like "/users/0/name".

JSON Patch (RFC 6902)

Standardized add, remove, replace, move, copy, and test operations.

JSON Merge Patch

RFC 7386 declarative merging for configuration overlays.

JSONPath Queries

SQL-like queries with wildcards: "$.users[*].name".

Streaming Parser

Process gigabyte-sized JSON files with constant memory.

Decimal Precision

Exact decimal values via simple_decimal - no floating-point artifacts.

Decimal Precision

For financial data or any values requiring exact representation, use put_decimal instead of put_real. This prevents floating-point artifacts like 19.99 becoming 19.989999999999998.

The Problem with REAL

-- Using put_real
obj.put_real (19.99, "price")
-- Output: {"price": 19.989999999999998}

The Solution with SIMPLE_DECIMAL

local
    price: SIMPLE_DECIMAL
do
    create price.make ("19.99")
    obj.put_decimal (price, "price")
    -- Output: {"price": 19.99}
end

Decimal API

Method Description
put_decimal (value, key) Store exact decimal value in object
decimal_item (key) Retrieve value as SIMPLE_DECIMAL
add_decimal (value) Add decimal to array
as_decimal Convert any JSON number to SIMPLE_DECIMAL

Documentation