Type inference refers to the automatic deduction of the type of an expression in a programming language. If some, but not all, type annotations are already present it is referred to as type reconstruction. The opposite operation of type inference is called type erasure.
It is a feature present in some strongly statically typed languages. It is often characteristic of, but not limited to, functional programming languages in general. Some languages that include type inference are ML, OCaml, Haskell, Scala, D, Clean, Opa and Go. It has lately been added (to some extent) to Visual Basic (starting with version 9.0), C# (starting with version 3.0) and C++11. It is also planned for Perl 6. The ability to infer types automatically makes many programming tasks easier, leaving the programmer free to omit type annotations while still permitting type checking.
Read more about Type Inference: Nontechnical Explanation, Technical Description, Example, Hindley–Milner Type Inference Algorithm
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