Don't do this

spread_operator_abuse.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:flutter/material.dart';

enum _Side { top, right, bottom, left }

extension SpreadBorder on Border {
  Iterable<MapEntry<_Side, BorderSide>> get sides {
    return () sync* {
      if (top != BorderSide.none) {
        yield MapEntry(_Side.top, top);
      }
      if (right != BorderSide.none) {
        yield MapEntry(_Side.right, right);
      }
      if (bottom != BorderSide.none) {
        yield MapEntry(_Side.bottom, bottom);
      }
      if (left != BorderSide.none) {
        yield MapEntry(_Side.left, left);
      }
    }();
  }

  static Border fromSides(Iterable<MapEntry<_Side, BorderSide>> parts) {
    BorderSide top;
    BorderSide right;
    BorderSide bottom;
    BorderSide left;

    for (final borderPart in parts) {
      switch (borderPart.key) {
        case _Side.top:
          top = borderPart.value;
          break;

        case _Side.right:
          right = borderPart.value;
          break;

        case _Side.bottom:
          bottom = borderPart.value;
          break;

        case _Side.left:
          left = borderPart.value;
          break;
      }
    }
    return Border(
      top: top,
      right: right,
      bottom: bottom,
      left: left,
    );
  }
}

final Border spreadBorder = SpreadBorder.fromSides([
  ...Border(
    left: BorderSide(color: Colors.pink),
    right: BorderSide(color: Colors.pinkAccent),
  ).sides,
  ...Border(
    top: BorderSide(color: Colors.blue),
    bottom: BorderSide(color: Colors.blueAccent),
  ).sides,
]).scale(5);

// boilerplate
void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Container(
        decoration: BoxDecoration(border: spreadBorder),
        child: Text(
                'You have pushed the button this many times:',
              ),),
              Text(
                '$_counter',
                style: Theme.of(context).textTheme.display1,
              ),
            ],
  
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}