Map expressions

[anton-trunov]

// or map<K, V> {
map {  
  k1: v1,
  ...
  [kn]: vn, // <- optional trailing comma
}

where k1, ..., kn -- key expressions, v1, ..., vn -- value expressions. If a simple literals and Identifiers are used as key expressions, we the syntax allows using them directly and if those are complex expressions, then the user needs to wrap those in square brackets (see an example below).

If all the key and value expressions can be computed at compile-time, it should translate into a constant cell primitive, a-la cell(...), otherwise we desugar something like let m: ... = map { [x + 1]: 42, [b]: y - 5, 24: 0 } as follows:

let m: ... = emptyMap();
m.set(x + 1, 42);
m.set(b, y - 5);
m.set(24, 0);

[verytactical]

Reference

[novusnota]

Reference

i.e. the current syntax of Struct and Message instantiations (instance expressions), but without the names.

To reduce ambiguity, I'd consider adding an explicit map<K, V> before, like:

let m = map<Int, Cell> {
    5: cell("..."),
    6: cell("..."),
};

Or maybe without <K, V>, since that can be inferred and because map is a reserved word:

let m: map<Int, Cell> = map {
    5: cell("..."),
    6: cell("..."),
};

And for the case of keys of Address type:

let m: <Address, Cell> = map {
    address("..."): cell("..."),
    address("..."): cell("..."),
    // or even this
    "EQ...": cell("..."),
};

Additionally, there's a question of whether this should still be considered a map<K, V> or Cell in the Tact's type system. I'd say this should be a map<K, V>, and if user wants to, they can add explicit .asCell() cast as such:

let c: Cell = map<Int, Cell> {
    5: cell("..."),
    6: cell("..."),
}.asCell();