Migrating from Older Versions

The C++ library is versioned according to the principles of Semantic Versioning. We define that the left-most non-zero component of the version is the major version, followed by the minor and optionally patch version. That means releases in the β€œ0.y.z” series treat changes in β€œy” as a major release, which can contain incompatible API changes, while changes in just β€œz” are minor. For example the release 0.1.6 is fully backwards compatible to 0.1.5, but it contains new functionality. The release 0.2.0 however is a new major version compared to 0.1.x and may contain API incompatible changes.

This guide lists all API incompatible changes between major versions and describes how you can migrate your application’s source code.

Migrating from Version 0.1.x to 0.2.0

In version 0.2.0 we have increased the minimum version of C++. You need to have a C++ compiler installed that supports C++ 20 or newer.

If you are building Slint from source, you need to make sure that your Rust installation is up-to-date. If you have installed Rust using rustup, then you can upgrade to the latest Version of Rust by running rustup update.

CMake interface

  • When using FetchContent, the SOURCE_SUBDIR has changed from api/sixtyfps-cpp to api/cpp

  • find_package(SixtyFPS) becomes find_package(Slint).

  • The SixtyFPS::SixtyFPS CMake target was renamed to Slint::Slint.

  • The sixtyfps_target_60_sources CMake command was renamed to slint_target_sources.

Some CMake options have been renamed:

Old Option New Option Note
SIXTYFPS_FEATURE_BACKEND_GL SLINT_FEATURE_BACKEND_GL_ALL Enable this feature if you want to use the OpenGL ES 2.0 rendering backend with support for all windowing systems.
SIXTYFPS_FEATURE_X11 SLINT_FEATURE_BACKEND_GL_X11 Enable this feature and switch off SLINT_FEATURE_BACKEND_GL_ALL if you want a smaller build with just X11 support.
SIXTYFPS_FEATURE_WAYLAND SLINT_FEATURE_BACKEND_GL_WAYLAND Enable this feature and switch off SLINT_FEATURE_BACKEND_GL_ALL if you want a smaller build with just wayland support.


Model::row_data returns now a std::optional<ModelData> and can thus be used with indices that are out of bounds.

This also means that Models must handle invalid indices and may not crash when a invalid index is passed in.

Old code:

float value = another_model->row_data(2);

New code:

// `another_model` is a model that contains floats.
std::optional<float> value = another_model->row_data(2);
if (value.has_value()) {
} else {
    // row index 2 is out of bounds

C++ Interpreter API


Callbacks declared in .slint markup can be invoked from C++ using slint::interpreter::ComponentInstance::invoke_callback() or slint::interpreter::ComponentInstance::invoke_global_callback(). The arguments to the callback at invocation time used to require the use of sixtyfps::Slice type. This was changed to use the C++ 20 std::span type, for easier passing.

Old code:

sixtyfps::Value args[] = { SharedString("Hello"), 42. };
instance->invoke_callback("foo", sixtyfps::Slice{ args, 2 });

New code:

slint::Value args[] = { SharedString("Hello"), 42. };
instance->invoke_callback("foo", args);


The Value::Type::Array has been replaced by Value::Type::Model