Typecast

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Typecasting is the concept, allowing to assign values of variables or expressions, that do not match the variable’s data type, virtually overriding Pascal’s strong typing system.

definition

Two flavors of typecasting are recognized:

implicit typecasting

If the complete range of values the source can be stored by the destination operand, an automatic – thus “implicit” – typecast occurs. For instance, all the values of a byte can be stored in an int64. Assigning a byte’s value to a int64 works without problems, since the missing 0-bits are filled in automatically, i.e. implicitly. The programmer does not have to insert any additional code.

explicit typecasting

If the source’s range of value does not fit into the destination operand’s range, the compiler will not compile the program, unless it is instructed to ignore this. There are two different explicit typecasts:

value typecast

A value typecast is done, by prepending a data type identifier and surrounding the expression to typecast with parentheses, like this: dataType(expression). Extraneous bits are just cut off. This approach is usually used, if there is absolute certainty, the actual value of the expression will fit into the destination. Occasionally this effect is also used instead of a modulo operation.

variable typecast

A variable typecast treats a variable as if it were a different type. Retrieving and storing the variable is done, as if it was the specified data type. Just as a value typecast, the data type identifier is prepended and parentheses surround, in this case, a variable identifier: dataTypeIdentifier(variableIdentifier). Unlike a value typecast, the variable typecast can occur on both sides of an assignment.

conversion versus typecasting

Type conversion is the ordered process of mapping the domain’s values to a co-domain, possibly triggering exceptions or run-time errors. This is done by properly defined functions. Bare typecasts on the other hand are always with brute force. They cut and push the bits 1:1 to the destination. However, you may define an operator overload redefining this behavior.

In some instances, you can convert values:

conversion opportunities

soure data type	target data type	type of type conversion	method
integer	real	implicit	assignment statement
real	integer	explicit	trunc cuts off fractional part round rounds fractional part
integer	string	explicit	sysUtils.intToStr
real	string	explicit	sysUtils.floatToStr sysUtils.floatToStrF
string	integer	explicit	sysUtils.strToInt
string	real	explicit	sysUtils.strToFloat
string	char	explicit	stringVariable[indexExpression]
char/ANSIChar/wideChar	string	implicit	assignment statement
char/ANSIChar	byte	explicit	ord byte(characterVariableOrExpression)
byte	char/ANSIChar	explicit	chr ANSIChar(byteVariableOrExpression)
enumerated type	string	explicit	system.Str(enumeratedVariableOrExpression, stringVariable) system.writeStr(stringVariable, enumeratedVariableOrExpression)

In other cases you manually have to perform explicit typecasts:

typecasting

source data type	target data type	type of type conversion	method
qWord	byte	explicit	byte(qWordVariableOrExpression)
qWord	word	explicit	word(qWordVariableOrExpression)
qWord	cardinal	explicit	cardinal(qWordVariableOrExpression)
qWord	longWord	explicit	longWord(qWordVariableOrExpression)
longWord	byte	explicit	byte(longWordVariableOrExpression)
longWord	word	explicit	word(longWordVariableOrExpression)
longWord	cardinal	implicit	assignment statement
int64	byte	explicit	byte(int64variableOrExpression)
int64	shortInt	explicit	shortInt(int64variableOrExpression)
comp	byte	explicit	byte(compVariableOrExpression)
comp	shortInt	explicit	shortInt(compVariableOrExpression)
comp	real	explicit	real(compVariableOrExpression)

caveats

• Explicit typecasts disable range checks altogether in the complete line of code.

see also

• “type casting (computer programming)” in the English Wikipedia
• § “value typecasts” in the FreePascal Reference guide
• § “variable typecasts” in the FreePascal Reference guide
• § “unaligned typecasts” in the FreePascal Reference guide
• operator overloading (especially the group of assignment operators, and § “routing”)