// run // Copyright 2026 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. package main import "fmt" var trace []int func f(x int) int { trace = append(trace, x) return x } func wantTrace(what string, want ...int) { if len(trace) != len(want) { fmt.Printf("%s: evaluation order %v, want %v\n", what, trace, want) panic(what) } for i, x := range want { if trace[i] != x { fmt.Printf("%s: evaluation order %v, want %v\n", what, trace, want) panic(what) } } trace = trace[:0] } func wantShape(what string, s []int, length, capacity int) { if len(s) != length || cap(s) != capacity { fmt.Printf("%s: len %d cap %d, want len %d cap %d\n", what, len(s), cap(s), length, capacity) panic(what) } } func main() { // The length is evaluated before the capacity, even though the // capacity is what gets rewritten. s := make([]int, f(1), f(3)) wantTrace("make", 1, 3) wantShape("make", s, 1, 3) // Same, for a capacity whose value comes from the length of a slice // literal rather than from a constant. s = make([]int, f(2), len([]int{0, 0, 0, 0})) wantTrace("make with len of literal", 2) wantShape("make with len of literal", s, 2, 4) // A two-operand make rewrites the length itself, which stays first. s = make([]int, f(4)) wantTrace("make without cap", 4) wantShape("make without cap", s, 4, 4) }