Difference between revisions of "Typecast"
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=== implicit typecasting === | === implicit typecasting === | ||
− | If the complete range of values the source | + | 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|<syntaxhighlight lang="pascal" inline>byte</syntaxhighlight>]] can be stored in an <syntaxhighlight lang="pascal" inline>int64</syntaxhighlight>. | For instance, all the values of a [[Byte|<syntaxhighlight lang="pascal" inline>byte</syntaxhighlight>]] can be stored in an <syntaxhighlight lang="pascal" inline>int64</syntaxhighlight>. | ||
Assigning a <syntaxhighlight lang="pascal" inline>byte</syntaxhighlight>’s value to a <syntaxhighlight lang="pascal" inline>int64</syntaxhighlight> works without problems, since the missing 0-bits are filled in automatically, i.e. implicitly. | Assigning a <syntaxhighlight lang="pascal" inline>byte</syntaxhighlight>’s value to a <syntaxhighlight lang="pascal" inline>int64</syntaxhighlight> works without problems, since the missing 0-bits are filled in automatically, i.e. implicitly. | ||
Line 102: | Line 102: | ||
| <syntaxhighlight lang="pascal" inline>string</syntaxhighlight> | | <syntaxhighlight lang="pascal" inline>string</syntaxhighlight> | ||
| explicit | | explicit | ||
− | | {{Doc|package=RTL|unit=system|identifier=writestr|text=<syntaxhighlight lang="pascal" inline>system.writeStr</syntaxhighlight>}}<syntaxhighlight lang="pascal" inline>(stringVariable, enumeratedVariableOrExpression)</syntaxhighlight> | + | | |
+ | * {{Doc|package=RTL|unit=system|identifier=str|text=<syntaxhighlight lang="pascal" inline>system.Str</syntaxhighlight>}}<syntaxhighlight lang="pascal" inline>(enumeratedVariableOrExpression, stringVariable)</syntaxhighlight> | ||
+ | * {{Doc|package=RTL|unit=system|identifier=writestr|text=<syntaxhighlight lang="pascal" inline>system.writeStr</syntaxhighlight>}}<syntaxhighlight lang="pascal" inline>(stringVariable, enumeratedVariableOrExpression)</syntaxhighlight> | ||
|} | |} | ||
In other cases you manually have to perform explicit typecasts: | In other cases you manually have to perform explicit typecasts: | ||
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== see also == | == see also == | ||
* [https://en.wikipedia.org/wiki/Type_casting_(computer_programming) “type casting (computer programming)”] in the English Wikipedia | * [https://en.wikipedia.org/wiki/Type_casting_(computer_programming) “type casting (computer programming)”] in the English Wikipedia | ||
− | * [https://www.freepascal.org/docs-html/ref/ | + | * [https://www.freepascal.org/docs-html/ref/refse84.html § “value typecasts”] in the FreePascal Reference guide |
− | * [https://www.freepascal.org/docs-html/ref/ | + | * [https://www.freepascal.org/docs-html/ref/refse85.html § “variable typecasts”] in the FreePascal Reference guide |
− | * [https://www.freepascal.org/docs-html/ref/ | + | * [https://www.freepascal.org/docs-html/ref/refse86.html § “<syntaxhighlight lang="pascal" inline>unaligned</syntaxhighlight> typecasts”] in the FreePascal Reference guide |
* [[Operator overloading|operator overloading]] (especially the group of assignment operators, and § “routing”) | * [[Operator overloading|operator overloading]] (especially the group of assignment operators, and § “routing”) |
Latest revision as of 02:44, 18 October 2023
│
Deutsch (de) │
English (en) │
français (fr) │
русский (ru) │
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:
soure data type | target data type | type of type conversion | method |
---|---|---|---|
integer
|
real
|
implicit | assignment statement |
real
|
integer
|
explicit | |
integer
|
string
|
explicit | sysUtils.intToStr
|
real
|
string
|
explicit | |
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 |
|
byte
|
char /ANSIChar
|
explicit |
|
enumerated type | string
|
explicit |
|
In other cases you manually have to perform explicit typecasts:
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”)