make（map）和map {}之间的区别

Question

Just wondering what the difference is between:

z := make(map[*test] string)

and

z := map[*test] string{}

am I imagining things or are they both not valid?

Answer 1

The Go Programming Language Specification

Making slices, maps and channels

The built-in function make takes a type T, which must be a slice, map or channel type, optionally followed by a type-specific list of expressions. It returns a value of type T (not *T). The memory is initialized as described in the section on initial values.

Call         Type T  Result
make(T)      map     map of type T
make(T, n)   map     map of type T with initial space for approximately n elements

Composite literals

Composite literals construct values for structs, arrays, slices, and maps and create a new value each time they are evaluated. They consist of the type of the literal followed by a brace-bound list of elements. Each element may optionally be preceded by a corresponding key.

map[string]int{}
map[string]int{"one": 1}

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make is the canonical form. Composite literals are a convenient, alternate form.

z := make(map[int]string)

and

z := map[int]string{}

are equivalent.