Radar · Go · #003 · Week 41 · Oct 5 – 11, 2026

Deprecate go/build.ArchChar(..)

Worth knowingstdlib

What changed: The proposal to mark go/build.ArchChar as deprecated was accepted.
Production impact: The source does not say.
Try it: Compile a program that calls build.ArchChar and observe the deprecation warning.
Source: github.com/golang/go/issues/75129

Understand it, then run it

go/build.ArchChar used to return a character that identified the CPU architecture. Since Go 1.5 the function always returns an error, and the proposal accepted in October 2026 marks it as deprecated. New code should not call it because it never gives useful information.

When you write Go programs you normally import go/build to inspect build constraints. The deprecated function is still present in the package, but the compiler will emit a deprecation warning and the function will still return an error.

The change means you can stop worrying about handling a special return value from ArchChar. Just avoid the call entirely and use other ways to detect the architecture, such as runtime.GOARCH.

Run it now

Todaygo

package main

import (
	"fmt"
	"go/build"
)

func main() {
	// ArchChar requires an architecture name argument.
	// Since Go 1.5 it always returns an error, demonstrating the deprecation.
	ch, err := build.ArchChar("amd64")
	if err != nil {
		fmt.Println("ArchChar error:", err)
		return
	}
	fmt.Printf("ArchChar returned: %c\n", ch)
}

What it printed when we ran it on Go 1.27.1

ArchChar error: architecture letter no longer used

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Written by gpt-oss-120b from the linked source · claims checked against the sources · human-reviewed