[bbodi]

What

A struct literal can now set an array field from an array value:

arr := [3]int{1, 2, 3}
b := Box{nums: arr} // was a compile error

Why

C brace initializers cannot copy an array. The generator therefore rejected any array field value that was not an array literal. Users had to declare the struct first and then assign the field.

How

The generator emits such a literal as a GNU statement expression. The expression fills a temporary with the other fields and copies each array with memcpy:

({ box _lit1 = {}; memcpy(_lit1.nums, arr, sizeof(so_int[3])); _lit1; })

The temporary initializer uses designators for every field, because the copied array fields are left out of it.

Limits

Three cases still require an array literal, and each case keeps the existing error:

• A package-level initializer, because C does not allow a statement expression at file scope.
• An anonymous struct literal, because the temporary needs a type name.
• An array literal element.

Taking the address of such a literal (&Box{nums: arr}) is a new error. A statement expression produces a value with no address.

Testing

• testdata/arrays covers keyed and positional fields, two array fields in one literal, array parameters, a call result as the value, a slice literal element, and a method call on the literal.
• New testdata/bad cases cover the package-level, anonymous struct, and address-of errors.
• go test ./... passes.

doc/spec.md describes the new rule and its limits.

[nalgeon]

Sorry, I'm against making the compiler more complicated in regards to array, slice, and struct handling — it's already complex enough. You can just use b.nums = arr.