Generics let a type or function work with values of different concrete types instead of being tied to one specific type. This removes casts and avoids separate CustomerList, IntList, or StringList implementations. section 3.2.3
F# often combines generics with type inference. You can provide a type argument explicitly, use a placeholder such as ResizeArray<_>, or let usage determine the type. Functions can also be automatically generalized when their arguments remain generic. section 3.2.3
A generic function can be written in two complementary styles:
- Write the type parameter explicitly when the intended type is important: combineElements<int> 1 2 3. section 3.2.3
- Let F# infer the generic behavior when the function is used consistently, as with combineElements 1 2 3. section 3.2.3
- Keep the arguments type-consistent: passing a string to combineElements<int> produces a type error rather than silently accepting incompatible data. section 3.2.3
A function with inferred generic parameters
let greetPerson name age = $"Hello, {name}. You are {age} years old" F# reports the parameters using generic type variables, allowing calls such as greetPerson "Fred" 21. Changing the arguments lets you test the function repeatedly. section 2.5.5
let combineElements<'T> (a:'T) (b:'T) (c:'T) = #1
let output = ResizeArray<'T>() #2
output.Add a
output.Add b
output.Add c
output
combineElements<int> 1 2 3 #3
Inspect the complete explicit-generic example, including the type parameter, generic ResizeArray, and typed function call. section 3.2.3
