Rules / Types, classes & roles / exception

X::Assignment::RO Reference

Exception thrown when trying to assign to something read-only

What it is #

Routines #

Signatures are reproduced from the documentation, including their declared return types. A routine listed here is part of the type's published interface; whether Raku++ implements it is a separate question, answered by the examples below.

method typename #

method typename(X::Assignment::RO:D: --> Str)

Returns Str.

Returns the type name of the value on the left-hand side

Examples, run three ways #

Every example below comes from the official documentation, together with the output that documentation asserts. Each was then executed by Rakudo and by Raku++ when this page was built. Where the three agree, one result is shown; where they do not, all three are — because which of them is wrong is exactly the information worth having.

1 all-differ · 1 no-output

class X::Assignment::RO is Exception {}

Not executed: the documentation states no expected output for this example.

sub f() { 42 };
f() = 'new value';  # throws an X::Assignment::RO
CATCH { default { put .^name, ': ', .Str } };
# OUTPUT: «X::Assignment::RO: Cannot modify an immutable Any␤»
Documentation
X::Assignment::RO: Cannot modify an immutable Any
Rakudo
X::Assignment::RO: Cannot modify an immutable Int (42)
Raku++
X::Assignment::RO: Target is not assignable

All three differ. Needs a human.

Not yet examined. Which of these is correct has not been established — do not treat either engine as settled here.