Why Can't Go's Short Variable Declaration Be Used at the Package Level?

Short Variable Declaration in Go: Restrictions at Package Level

Consider the following code:

package main

var a = 3

...

This declaration is valid in Go, assigning the value 3 to the variable a. However, the following declaration is forbidden:

package main

a := 3

...

Why this discrepancy? Why can't short variable declaration be utilized outside a function?

The reason lies in Go's parsing mechanism. According to Ian Lance Taylor, a contributor to the development of Go, this restriction ensures simplicity in parsing. By requiring every declaration at the package level to begin with a keyword, the parser can efficiently identify and interpret declarations without ambiguity. This approach simplifies and expedites the parsing process. Thus, short variable declaration, which lacks an explicit keyword, is not permitted at the package level in Go.

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