This is allowed:
package main
var a = 3
...
But this isn't:
package main
a := 3
...
Why not? Why couldn't short variable declaration outside a function be treated regular declaration without a type? Just to simplify parsing?
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3 Answers
42
According to Ian Lance Taylor in this thread shortly after the public announcement:
At the top level, every declaration begins with a keyword. This simplifies parsing.
Gustavo Niemeyer
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2Is there any explanation anywhere as to how does this help parsing ? – vadasambar Jun 18 '19 at 11:53
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1Still, no explanation on why and how exactly it simplifies parsing... – IvanD Nov 21 '20 at 02:19
8
To quote from The Go Programming Language Specification:
Short variable declarations may appear only inside functions. In some contexts such as the initializers for "if", "for", or "switch" statements, they can be used to declare local temporary variables.
You can think of var statement like const, type, and func, in the package level you have to specify what's kind of statement you are declaring.
Well , it's not a real shorthand , a, b := 12 can't compile, var a,b = 12 do.
Salah Eddine Taouririt
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3
Outside a function, every statement must begin with a keyword (var, func, and so on), and so the := construct is not available.
See here. Hope it helps.
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Hi @Matt, just curious, what was the reason that you edited my answer? could you please share your feedback so that I can improve my answers in future. thank you. – srini May 27 '15 at 19:15