const if语句是否与Go中的#ifdef宏具有相同的功能？

Question

There's no text preprocessing in Go. Like Java and others like it, if I want to remove a block of code I can use a const value and surround the code with an if.

If I do this, does the compiler optimise the code from the AST and out of the generated code? Or is the condition executed each time?

EDIT: If I want to replicate #ifdef what's the best way to do it?

Answer 1

If statements with constant conditions are not the same as #ifdef because the code inside is always compiled no matter what. However, the compilers do optimize it away when possible. Consider this program:

package main

import (
    "fmt"
)

func main() {
    if false {
        fmt.Println("Hello, world!")
    }
}

If we run go tool 6g -S test.go, here's the assembly output for the main function:

--- prog list "main" ---
0000 (test.go:7) TEXT    main+0(SB),$40-0
0001 (test.go:11) RET     ,

The dead code is gone so all it does is return.

If you do need to actually conditionally compile parts of your code, it's best to do it through the build system.