In programming languages, type erasure refers to the compile-time

Compile time

In computer science, compile time refers to either the operations performed by a compiler , programming language requirements that must be met by source code for it to be successfully compiled , or properties of the program that can be reasoned about at compile time.The operations performed at...

 process by which explicit type annotations

Type system

A type system associates a type with each computed value. By examining the flow of these values, a type system attempts to ensure or prove that no type errors can occur...

 are removed from a program, before it is executed at run-time. An operational semantics

Operational semantics

In computer science, operational semantics is a way to give meaning to computer programs in a mathematically rigorous way. Operational semantics are classified into two categories: structural operational semantics formally describe how the individual steps of a computation take place in a...

 that does not require programs to be accompanied by types is called a type-erasure semantics, to be contrasted with a type-passing semantics. The possibility of giving a type-erasure semantics is a kind of abstraction principle

Abstraction principle (programming)

In software engineering and programming language theory, the abstraction principle is a basic dictum that aims to reduce duplication of information in a program whenever practical by making use of abstractions provided by the programming language or software libraries...

, ensuring that the run-time execution of a program does not depend on type information.

The reverse operation is called type inference

Type inference

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....

. Though type erasure can be used as an easy way to define typing over implicity typed languages (an implicitly typed term is well-typed if and only if

If and only if

In logic and related fields such as mathematics and philosophy, if and only if is a biconditional logical connective between statements....

it is the erasure of a well-typed explicitly typed lambda term), it does not always lead to an algorithm to check implicitly typed terms.