go - Why use a statement inside an "if" statement? -

go - Why use a statement inside an "if" statement? -

the go tour shows illustration have statement in same line "if" statement , explain this: the if statement can start short statement execute before condition.

func pow(x, n, lim float64) float64 { if v := math.pow(x, n); v < lim { homecoming v } homecoming lim }

i don't see need syntax , find confusing. why not write v := math.pow(x, n) in previous line?

the reason i'm asking i'm finding out, syntax finds way go language after careful consideration , nil seems there out of whim.

i guess actual question be: specific problem trying solve using syntax? gain using didn't have before?

there many utilize cases , not think feature tackles specific problem rather pragmatic solution problems encounter when code in go. basic intentions behind syntax are:

proper scoping: give variable scope needs have proper semantics: create clear variable belongs specific conditional part of code

some examples remember off top of head:

limited scopes:

if v := computestuff(); v == expectedresult { homecoming v } else { // v valid here } // carry on without bothering v

error checking:

if perr, ok := err.(*os.patherror); ok { // handle path error }

or more general, type checking:

if somestruct, ok := someinterface.(*somestruct); ok { // someinterface *somestruct. }

key checking in maps:

if _, ok := mymap[somekey]; ok { // key exists }

if-statement go