Go golang, syntax error: unexpected ++, expecting :, why can't I put i++ in index of slice?

Question

func test(args ...string) { var msg map[string] interface{} i := 0 msg["product"] = args[i++] msg["key"] = args[i++] msg["signature"] = args[i++] msg["string_to_sign"] = args[i++] } go build utils.go after compile, I get the error message ./utils.go:28: syntax error: unexpected ++, expecting : ./utils.go:28: missing statement after label ./utils.go:29: syntax error: unexpected ++, expecting : ./utils.go:30: syntax error: unexpected ++, expecting : ./utils.go:31: syntax error: unexpected ++, expecting : ./utils.go:36: syntax error: unexpected ++, expecting : ./utils.go:37: syntax error: unexpected ++, expecting : why can't I put i++ in index of slice? is there any limitation in index of slice?

Gopher · Accepted Answer

Go Frequently Asked Questions (FAQ) Why are ++ and -- statements and not expressions? And why postfix, not prefix? Without pointer arithmetic, the convenience value of pre- and postfix increment operators drops. By removing them from the expression hierarchy altogether, expression syntax is simplified and the messy issues around order of evaluation of ++ and -- (consider f(i++) and p[i] = q[++i]) are eliminated as well. The simplification is significant. As for postfix vs. prefix, either would work fine but the postfix version is more traditional; insistence on prefix arose with the STL, a library for a language whose name contains, ironically, a postfix increment. The Go Programming Language Specification IncDec statements The "++" and "--" statements increment or decrement their operands by the untyped constant 1. As with an assignment, the operand must be addressable or a map index expression. IncDecStmt = Expression ( "++" | "--" ) . The following assignment statements are semantically equivalent: IncDec statement Assignment x++ x += 1 x-- x -= 1 Write, func test(args ...string) { var msg map[string]interface{} i := 0 msg["product"] = args[i] i++ msg["key"] = args[i] i++ msg["signature"] = args[i] i++ msg["string_to_sign"] = args[i] } Which, in your particular case, simplifies to, func test(args ...string) { var msg map[string]interface{} msg["product"] = args[0] msg["key"] = args[1] msg["signature"] = args[2] msg["string_to_sign"] = args[3] }

Go Language

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