Why Can\'t I Use `var` to Declare Variables in Go\'s For Loop Initialization?

Variable Initialization in For Loop's Initialization Statement

Wondering why you can declare variables in the initialization statement of a for loop using the shorthand i := 0 but not with var i = 0?

The Go programming language specification stipulates that the initialization statement in a for loop can include a short variable declaration (i := 0). This is a concise way to declare a variable and assign an initial value in a single statement. However, full variable declarations using var are not allowed in this context.

The reason for this design choice is likely to keep the syntax of the language simple and consistent. For loops are commonly used for iterating over sequences, and the shorthand notation allows for efficient variable initialization and assignment within the loop.

Despite the restriction on using var in the initialization statement, there are other ways to declare a variable with a specific type and use it in the loop. For instance, you can declare the variable outside the loop:

var i int64 = 0
for ; i < 10; i++ {
  // ...
}

Alternatively, you can cast the variable during the initialization:

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

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