Value Assignments

A value assignment stores a value by a name on the stack. They can be placed in source files, building code, module functions or workbench functions.

The following example defines the variable a which from then is a reserved name within the scope in which it was defined (locality). In this case the source code file itself:

// source code file is the scope of a and b

use std::debug::*;

a = 5;
b = a * 2;
assert_eq([a, 5]);
assert_eq([b, 10]);

Locality

If you place a value assignment into a scope (using brackets {}), the defined value is only available within that specific scope:

// source code file is the topmost scope #0

use std::debug::*;

// define a within scope #0
a = 5;
assert_eq([a, 5]);

// scope #1
{
    // define b within scope #1
    b = a * 2;
    // of course b is available at this point
    assert_valid("b");

    // scope #2
    {
        // b is available in scope #2 because #2 is within #1
        assert_valid("b");
    }
}

// a is still available
assert_valid("a");
// b not known here anymore
assert_invalid("b");

Restrictions

No Shadowing

So-called "shadowing" (reusing a name) is prohibited. This restriction is highly intentional because µcad follows a concept of strict immutability¹ of all value definitions.

So another assignment of a variable with the same name without an additional scope is prohibited.

a = 5;
a = a * 2; // error: a already defined in this scope

Even if using anonymous scopes this does not change.

a = 5;
{
    a = a * 2;
    std::debug::assert_eq([a, 10]);
}

[!NOTE] Anonymous scopes do not open new namespaces in µcad. This is different in a lot of other languages!

Not in modules

Value assignments are not available in modules:

mod my_module {
    a = 1; // error
}

Not in initialization code

Value assignments are not available in workbenches' initialization code:

sketch MySketch() {
    a = 1; // error
    init(_x: Scalar) {}
}

MySketch();

1. Reusing names would undercut the ability to connect identifiers to values (labeling). ↩