This is a demo of a proposed exception to warning S1021 in `staticcheck`

staticcheck_s1021.go

// Package main is a toy app demoing a defect in `staticcheck`s test for "S1021"
package main

import "fmt"

// Foo is a sample custom type
type Foo struct {
	Value    int
	runabble func()
}

// NewFoo creates a new Foo
func NewFoo(v int, r func()) *Foo {
	return &Foo{
		Value:    v,
		runabble: r,
	}
}

// RunNow executes runnable
func (f *Foo) RunNow() {
	f.runabble()
}

// Bar is another sample custom type
type Bar struct {
	Value int
}

// ScaleFoo scales the value of the given Foo by this Bar
func (b *Bar) ScaleFoo(f *Foo) {
	f.Value *= b.Value
}

func main() {
	myBar := &Bar{Value: 5}
	// This is where we expect `staticcheck` to report a S1021 warning,
	// but in this case it shouldn't, because defining `myFoo` with `:=`
	// on line 42 would prevent it from being used on line 43 where it isn't
	// defined yet.
	var myFoo *Foo
	myFoo = NewFoo(7, func() {
		myBar.ScaleFoo(myFoo)
	})
	fmt.Printf("After creating myFoo, it looks like this: %#v\n", *myFoo)
	myFoo.RunNow()
	fmt.Printf("After running RunNow() on it, it looks like this: %#v\n", *myFoo)
}