stringable.go

     1  // run
     2  
     3  // Copyright 2021 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  package main
     8  
     9  import (
    10  	"fmt"
    11  	"strconv"
    12  	"strings"
    13  )
    14  
    15  type Stringer interface {
    16  	String() string
    17  }
    18  
    19  // StringableList is a slice of some type, where the type
    20  // must have a String method.
    21  type StringableList[T Stringer] []T
    22  
    23  func (s StringableList[T]) String() string {
    24  	var sb strings.Builder
    25  	for i, v := range s {
    26  		if i > 0 {
    27  			sb.WriteString(", ")
    28  		}
    29  		sb.WriteString(v.String())
    30  	}
    31  	return sb.String()
    32  }
    33  
    34  type myint int
    35  
    36  func (a myint) String() string {
    37  	return strconv.Itoa(int(a))
    38  }
    39  
    40  func main() {
    41  	v := StringableList[myint]{myint(1), myint(2)}
    42  
    43  	if got, want := v.String(), "1, 2"; got != want {
    44  		panic(fmt.Sprintf("got %s, want %s", got, want))
    45  	}
    46  }
    47
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