[kazinator]

In C, cast converts a value to another type (or a more or less qualified version of the same type). What that conversion means depends on the source and destination type.

A cast of insert a conversion that wouldn't take place:

  1/2 vs 1/(double)2

or coerce a conversion that otherwise requires a diagnostic:

  bar *b = 0;
  foo *f = (foo *) b;

Loosely speaking, casting is another name for coercion, which refers to making a conversion happen that might not otherwise.

[shakna]

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.

[kazinator]

The difference between implicit conversion and explicit is just syntactic sugar: do you have to put some visible tokens into the code to allow a conversion to happen, or not.

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.

[shakna]

I really wouldn't call something you need to write, to make something happen, "syntactic sugar".

Otherwise types are just sugar. Indicies are just sugar. Lists are just sugar.

[fc417fc802]

It's the other way around. Implicit conversion is syntactic sugar for explicit conversion. Sugar is anything that is functionally identical, just notated more conveniently.

That said, I think you're correct about the casting versus conversion distinction. Languages frequently overload established terminology with slightly modified variants and it's incredibly confusing.