Why Can\'t I Initialize Go Constants with Function Calls?

Constants in Go: Declaring Constant Variables with Initialization

In Go, constants provide constant values that cannot be changed during program execution. To declare a constant, the keyword const is used. However, initializing constants with function calls is not permitted.

Consider the example:

const KILO = math.Pow10(3)

This will result in an error: "const initializer math.Pow10(3) is not a constant."

Why Constants Cannot Be Initialized with Function Calls

Constants are evaluated at compile time, whereas function calls occur at runtime. Therefore, it is not possible to initialize constants with function calls, as the function call's result is not known until runtime.

Exception for Built-in Functions

Some built-in functions, such as unsafe.Sizeof(), can be used in constant declarations as they can be evaluated at compile time. However, most function calls cannot be used in constant declarations.

Alternatives for Initializing Constants

To initialize constants with values that cannot be evaluated at compile time, use variables instead. For example:

var KILO = math.Pow10(3)

In this case, the variable KILO will be initialized with the result of the math.Pow10(3) call at runtime.

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