infix

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A lightweight Dart library that elegantly solves code nesting problems using infix operators.

Overview

When building nested Widget trees or data structures, you often encounter "callback hell" or the "pyramid problem". The traditional nested approach:

// ❌ Too much nesting makes code hard to read
import 'package:flutter/material.dart';

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Flutter Infix Example')),
      body: Center(
        child: ColoredBox(
          color: Colors.amberAccent,
          child: Padding(
            padding: const EdgeInsets.all(16.0),
            child: Card(
              child: Text('Nested Widgets'),
            ),
          ),
        ),
      ),
    );
  }
}

Encapsulating deep nesting as a Widget can help, but often such Widgets are only used once, lack reusability, and naming/definition becomes an extra burden.

By observing the nesting, we see that some Widgets act as infix roles (like Padding, Center, Card), while others are leaf nodes (like Text). By distinguishing these two roles, we can avoid excessive nesting.

The infix library provides a solution using - (wrap/via/-/|) for infix Widgets and > for leaf Widgets:

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Flutter Infix Example')),
      body:
          wrap((c) => Center(child: c))
              .wrap((c) => ColoredBox(color: Colors.amberAccent, child: c))
              .wrap((c) => Padding(padding: const EdgeInsets.all(16.0), child: c))
              .wrap((c) => Card(child: c)) >  // infix applies to leaf Widget
          Text('Nested Widgets'),
    );
  }
}

It's also very easy to adjust the nesting order and insert new infix Widgets. In VS Code, you can use Alt+Up/Down to adjust the order.

This is similar to Python's decorator syntax:

@Center
@ColoredBox(Colors.amberAccent)
@Card
def build(): return Text('Hello, Infix!')

For more usage examples, see example/example.md

via

The purpose is to adapt scenarios where the child and parent types are inconsistent. In this case, the child type cannot be inferred and must be specified explicitly.

via((App c) => PrarentApp(child: c))
.via((Child c) => App(child: c))
> Leaf()