Why Can\'t I Use a Function Call to Initialize a Constant in Go?

Initializing Constant Variables

When attempting to assign a function call to the constant KILO, you encounter an error. This is because constant declarations cannot contain function calls, as they must be evaluated at compile time. Constant expressions include literal values, constant identifiers, and certain built-in functions like unsafe.Sizeof().

According to the Go specification, "Constant expressions may contain only constant operands and are evaluated at compile time." So, functions generally cannot be called within constant declarations.

To initialize the constant KILO, use an integer or floating-point literal instead of a function call:

const Kilo = 1000  // Integer literal

Or:

const Kilo = 1e3   // Floating-point literal

Alternatively, you can create a variable instead of a constant if you need to use a function to calculate the value:

var Kilo = math.Pow10(3)

Note that some built-in functions, like unsafe.Sizeof(), cap, and len, can be used in constant declarations. However, function calls that involve runtime execution, like math.Pow10(), are not allowed.

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