feat(docs): destructuring statement

[novusnota]

Issue

A follow-up docs PR for issue #298 and PR #856.

Checklist

• I have updated CHANGELOG.md
• I have run the linter, formatter and spellchecker
• I did not do unrelated and/or undiscussed refactorings

[anton-trunov]

Awesome stuff, I especially liked the note about the unsupported nested structs. Let's fix one small inaccuracy and we are good to go

[anton-trunov]

It's not exhaustive, you can say let Two { first } = s which is equivalent to let Two { second: _, first } = s (as in the example below)

[novusnota]

Curiosly, that depends. The following example (taken from docs):

struct Two { first: Int; second: String }

fun discard(s: Two) {
    let Two { first } = s;
    // ^^^^^^^^^^^^^^^^^^^
}

Will report an error: "Cannot evaluate expression to a constant: destructuring assignment expected 2 fields, but got 1".

But if one would place the same destructuring statement in the receive() function, there would be no such error:

struct Two { first: Int; second: String }
message HasTwo { s: Two }

contract Example {
   receive() {}
   receive(msg: HasTwo) {
       // Almost the same line as in the previous example
       let Two { first } = msg.s;
       
       // No errors before or here
       dump(first);
   }
}

[Gusarich]

Oh! I forgot to remove this error from interpreter. I'll open a fix PR:

tact/src/interpreter.ts

Lines 1468 to 1475 in 9522f81

	if (ast.identifiers.size !== Object.keys(val).length - 1) {
	throwErrorConstEval(
	`destructuring assignment expected ${Object.keys(val).length - 1} fields, but got ${
	ast.identifiers.size
	}`,
	ast.loc,
	);
	}

[Gusarich]

LGTM!

[jeshecdom]

Love the explanation. It is very clear.

[jeshecdom]

Once the associated PR #969 is approved, I will approve this PR.