Deprecated Properties

The @deprecated annotation marks a property declaration as deprecated. Whenever the property is accessed from outside the component that declares it, the compiler emits a warning that points to the replacement. This lets a component evolve its public API while giving users a migration path instead of a hard break.

Note: @deprecated is experimental and subject to change.

Syntax

Prefix a property declaration with @deprecated. Without an argument, the property must have a two-way binding, and the replacement is derived from its target:

@deprecated in-out property <int> old-prop <=> new-prop;

slint

An access to old-prop then warns with Please use 'new-prop' instead.

Pass a string literal to provide a custom message when there is no single replacement property:

@deprecated("Compute it from 'new-prop' instead") in-out property <int> older-prop: 42;

slint

Example

component Inner {
    in-out property <int> new-prop;
    @deprecated in-out property <int> old-prop <=> new-prop;

    // No warning: accesses within the declaring component are fine.
    in-out property <int> internal: old-prop;
}

export component Example {
    inner := Inner {
        new-prop: 42;
    }

    // Warning: The property 'old-prop' has been deprecated. Please use 'new-prop' instead
    property <int> value: inner.old-prop;
}

slint

Rules

• @deprecated can only be applied to property declarations.
• Without a message, the declaration must use a two-way binding (<=>) so the replacement can be derived from its target. Otherwise, the compiler reports an error.
• The message must be a plain string literal, without any \{} expressions.
• Accessing a deprecated property is only a warning, never an error, so existing code keeps compiling.
• Accesses from within the declaring component do not warn, since that component still needs to implement the property.