Why Can\'t I Declare a Typed Variable in a Go For Loop\'s Initialization Statement?

Variable Declaration in the Initialization Statement of a For Loop

In Go, the syntax for a for loop allows declaring a variable in the initialization statement. However, this declaration must follow a specific format.

The question arises as to why a variable cannot be declared with a specific type in the initialization statement, such as for var i int64 = 0; i < 10; i {}. Instead, the code requires a separate variable declaration (var i int64) followed by an assignment statement (i = 0).

The language specification for the for loop explains that the init statement can only be a short variable declaration, which is an assignment of the form i := 0. It cannot be a full variable declaration using var.

This restriction likely stems from the desire for language simplicity. By limiting the initialization statement to a short variable declaration, the syntax becomes more concise and less confusing.

However, it is worth noting that there is a workaround to declare a variable with a specific type in the initialization statement. This can be done using an explicit type conversion:

for i := int64(0); i < 10; i++ {
    // i here is of type int64
}

In this example, the variable i is explicitly cast to type int64 in the initialization statement.

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