On Thursday, 6 February 2020 at 21:41:33 UTC, Lim wrote: > According to current Spec: "If the TemplateArgument is one > token long, the parentheses can be omitted", all two examples I > showed are legal. One token, not one argument. `a:b` and alike are three tokens long. See https://dlang.org/spec/lex.html#tokens