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Implicit conversion, which is what you're mostly referring to here, is not required. It happens in some languages, and not others. Because I'm tired, and this is a very basic topic, I'm afraid I'm just going to rip from Wikipedia: > In most ALGOL-like languages, such as Pascal, Modula-2, Ada and Delphi, conversion and casting are distinctly different concepts. In these languages, conversion refers to either implicitly or explicitly changing a value from one data type storage format to another, e.g. a 16-bit integer to a 32-bit integer. The storage needs may change as a result of the conversion, including a possible loss of precision or truncation. The word cast, on the other hand, refers to explicitly changing the interpretation of the bit pattern representing a value from one type to another. For example, 32 contiguous bits may be treated as an array of 32 Booleans, a 4-byte string, an unsigned 32-bit integer or an IEEE single precision floating point value. Because the stored bits are never changed, the programmer must know low level details such as representation format, byte order, and alignment needs, to meaningfully cast. > In the C family of languages and ALGOL 68, the word cast typically refers to an explicit type conversion (as opposed to an implicit conversion), causing some ambiguity about whether this is a re-interpretation of a bit-pattern or a real data representation conversion. More important is the multitude of ways and rules that apply to what data type (or class) is located by a pointer and how a pointer may be adjusted by the compiler in cases like object (class) inheritance. |
Implicit conversion can be seen as the compiler deciding among several possible conversions (or possibly just one) and inserting the coercion/casting operator into the intermediate code to make it happen.
(Of course, this can be a run-time decision based on dynamic types also, but the reasoning is the same. E.g. the run-time sees that a plus operation is adding an integer and float, and can either signal an error (requiring the program to be repaired by inserting a conversion operation into the expression), or just do that conversion, like the integer operand to float.