Inlay Hints in C++

Parameter name hints

Parameter name hints are editor adornments that show parameter names next to the corresponding arguments at method calls. They can help you find your way through long (and sometimes nested) lists of parameters in function calls and aggregate initialization.

In the example below, parameter name hints help to spot the fact that height and width arguments are mixed up:

Parameter name hints show the names of the members you are initializing and help disentangle complex aggregate initializations in C++17 and later:

Parameter name hints are available in dependent code as well:

Namespace name hints

Namespace name hints at the end of namespace definitions could be helpful if you are not following the LLVM or Google guidelines, which suggest adding namespace in a comment after the namespace closing bracket:

Preprocessor directive hints

Preprocessor directive hints help you quickly understand how conditional inclusions (#ifdef, #ifndef, #if, #endif, #else, and #elif) correspond to macro definitions:

Type name hints

Type name hints help you when a type is deduced automatically by the compiler from the surrounding code. JetBrains Rider provides type name hints for auto variables, function and lambda return types, in structured bindings, dependent code, and after function calls.

Auto variables

This kind of hints is available for variables with automatically deduced type, which use the auto or decltype(auto) type specifiers. By default, the hint will be hidden if the deduced type is clear from the initializer expression, for example when the initializer is a constructor call, a constant, or an explicit cast.

Function and lambda return types

The return types of functions and lambdas can be automatically deduced from the return statement when they are omitted in the code:

Structured bindings

In C++17’s structured binding declarations, type hints are especially useful since the type of a structured binding cannot be explicitly specified.

Dependent code

Type hints also work for dependent code but note that they can affect the performance. In this case, disable the dependent code hints on the Editor | Inlay Hints | C++ | Type Name Hints page of JetBrains Rider settings Ctrl+Alt+S.

Function calls

With the default settings, this kind of type hint is shown only after multiline chained member functions calls.

Type conversion hints

Type conversion hints help make hidden implicit conversions visible, so that you are aware of potential performance and correctness implications.

JetBrains Rider displays hints for different kinds of class type conversions, including object copying, object initialization using converting constructors or aggregate initialization, and calls to conversion operators.

You can also enable hints for standard conversions between built-in types, for example, conversions between numeric types that might lose precision or change the signedness of the type.