CODEWITHSUNDEEP
rust
pm100
pm100

Reputation: 50110

Can I unstring a literal in a macro?

I want to make a macro that does this

mac1!("foo", x)

emits

foo(x)

is it even possible?

Upvotes: 0

Views: 141

Answers (1)

user2722968
user2722968

Reputation: 16475

No, it's not possible. By the time the macro is expanded, the matching is done on the fact that "foo" is an expression (or a literal). The compiler does not distinguish between an expression like "foo" in your example and 123u8, 1 + 2, foo() or { let f = fs::read("foo.txt"); ... } as all of those are expressions. All the macro-by-example knows is that the first parameter is any kind of valid expression and it can't look deeper into it, because the compiler doesn't know what a "type" or a "value" is at this point.

You can use a procedural macro, which can use a parameter's value to generate new tokens, including identifiers.

Upvotes: 2

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