初始化const变量 [英] Initialize const variable

问题描述

如何使用 const 类型初始化 KILO 变量？

How can I initialize KILO variable with const type?

const KILO = math.Pow10(3)

因为我有错误

const initializer math.Pow10(3) is not a constant

推荐答案

常量声明不能包含函数调用（某些例外，请参阅下文），必须对其进行求值

Constant declarations cannot contain function calls (with some exceptions, see below), they must be evaluated at compile time while a function call is carried out at runtime.

在规范：常量：

常量值由符文， integer ，浮点，虚构，或字符串文字，表示标识符常量，常量表达式，转换，其结果是一个常量，或者是某些内置函数的结果值，例如 unsafe.Sizeof 应用于任何值，上限或 len 应用于某些表达式， real 和 imag

A constant value is represented by a rune, integer, floating-point, imaginary, or string literal, an identifier denoting a constant, a constant expression, a conversion with a result that is a constant, or the result value of some built-in functions such as unsafe.Sizeof applied to any value, cap or len applied to some expressions, real and imag applied to a complex constant and complex applied to numeric constants.

并引用到 complex 常量，将复数应用于数字常量。来自规范：常量表达式：

And quoting from Spec: Constant expressions:

常量表达式只能包含常量操作数，并在编译时求值。

请注意，有一些内置函数可以在常量声明中调用，例如 unsafe.Sizeof（），

Note that there is a small set of (builtin) functions that may be called in constant declarations such as unsafe.Sizeof(), but generally you can't do that.

所以只需使用

const Kilo = 1000  // Integer literal

Or

const Kilo = 1e3   // Floating-point literal

有关Go常量的广泛介绍，请阅读博客文章：常量

For an extensive introduction to Go constants, read blog post: Constants

如果由于某种原因您确实需要调用函数，则无法将其存储在常量中，它必须是变量，例如：

If for some reason you do need to call a function, you cannot store it in a constant, it must be a variable, e.g.:

var Kilo = math.Pow10(3)

另请参阅相关的紧凑地将10的幂作为常数写。

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