defaultT

defaultT is a conventional label used in generic programming to denote a type parameter that has a default type. It is not a language keyword itself, but a naming pattern commonly seen in documentation and example code to illustrate the concept of default type arguments and how they affect type inference and instantiation.

In languages that support default type arguments, a generic or template can declare a type parameter with a fallback type. For example, in C++: template<class T = int> struct Box { T value; }; Box<> b; // T defaults to int. In Rust: struct Box<T = i32> { value: T } let b: Box = Box { value: 0 }; In TypeScript: class Box<T = any> { value: T; } The exact syntax varies by language, but the principle remains: omitting the type argument uses the default.

Benefits of defaultT-like patterns include reduced boilerplate for common cases, simpler instantiation, and smoother evolution of APIs by allowing new type parameters to be added without breaking existing code. Designers must consider constraints on the default type (such as bounds or interfaces) and potential impacts on type inference and readability. A poorly chosen default can obscure type errors or hide mismatches, so defaults should be chosen to be safe and broadly useful.

History and usage: the idea of default type arguments emerged with the broader adoption of generics and templates. defaultT serves as an instructional label rather than a formal language construct, with actual syntax defined by each language. See also: Default type argument, Generic parameter, Type parameter default.