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(Or "coercion") The abilty of some compilers to automatically insert type conversion functions where an expression of one type is used in a context where another type is expected.
A common example is coercion of integers to reals so that an expression like sin(1) is compiled as sin(integerToReal(1)) where sin is of type Real -> Real.
A coercion is usually performed automatically by the compiler whereas a cast is an explicit type conversion inserted by the programmer.
See also subtype.