Operator overloading is a very nice feature of the Delphi language.
However. the Delphi documentation on Operator overloading is not completely right.
Below is my table of what I found out so far, and some notes.
It is part of my “Nullable types in Delphi” session that I gave on some conferences.
The downloads for that session contain more detailed information.
This is just an abstract to get you going and a try to answer this operator overloading question on Stackoverflow.
Download the full presentation to get more in depth information.
Let me know if you need more information.
Notes
Operator overloading
Add your own “behaviour” to operators
- Win32: Works only for records, not classes!
- An operator and the operand(s)
are being implemented worden by a “class operator”;
this is a kind of class method with name and argumen(s)
Example:
- Multiplication X : = A * B;
- Operator: *
- Name: Multiply
- Operands: 2 -> two parameters
type
TMyRecord = record
class operator Multiply(A, B: TMyRecord): TMyRecord;
end;
Documentation is not correct!
- http://docs.embarcadero.com/products/rad_studio/delphiAndcpp2009/HelpUpdate2/EN/html/devcommon/operatoroverloads_xml.html
- http://docwiki.embarcadero.com/RADStudio/en/Operator_Overloading_(Delphi)
- Win32 only records; .NET classes and records
- BitwiseNot does not exist (use LogicalNot)
- At least 1 operand must be of the same type as your record data type
- Result type may be anything
Watch the result type of comparison operators!
Tips:
- Some operators should be overloaded pair-wise
= and <>
shl and shr
< and >=
> and <=
dec and inc
+ and -
/ and *
div and mod - Prefer Explicit over Implicit operators
- Beware of the built-in type coercion (implicit operators)
- e.g
- Byte to Integer;
- Integer to Double;
- Variants from/to anything!
Table of operators
| operator | # | usage | name | cagetory | * |
| and | 2 | R := A and B; | BitwiseAnd | bit | |
| not | 1 | R := not A; | //BitwiseNot | bit | glitch: does not exist! |
| or | 2 | R := A or B; | BitwiseOr | bit | |
| xor | 2 | R := A xor B; | BitwiseXor | bit | |
| () cast | 1 | R := TValue(A); | Explicit | conversion | |
| := | 1 | R := A; | Implicit | conversion | |
| operator | # | usage | name | category | * |
| round | 1 | R := Round(A); | Round | function | |
| trunc | 1 | R := Trunc(A); | Trunc | function | |
| and | 2 | R := A and B; | LogicalAnd | logical | |
| not | 1 | R := not A; | LogicalNot | logical | |
| or | 2 | R := A or B; | LogicalOr | logical | |
| xor | 2 | R := A xor B; | LogicalXor | logical | |
| operator | # | usage | name | category | * |
| + | 2 | R := A + B; | Add | binary | |
| / | 2 | R := A / B; | Divide | binary | |
| div | 2 | R := A div B; | IntDivide | binary | |
| mod | 2 | R := A mod B; | Modulus | binary | |
| * | 2 | R := A * B; | Multiply | binary | |
| - | 2 | R := A – B; | Subtract | binary | |
| operator | # | usage | name | category | * |
| shl | 2 | R := A shl B; | LeftShift | binary | name is confusing |
| shr | 2 | R := A shr B; | RightShift | binary | name is confusing |
| - | 1 | R := -A; | Negative | binary | |
| + | 1 | R := +A; | Positive | binary | |
| dec | 1 | Dec(A); | Dec | self | |
| inc | 1 | Inc(A); | Inc | self | |
| operator | # | usage | name | category | * |
| = | 2 | R := A = B; | Equal | comparison | |
| > | 2 | R := A > B; | GreaterThan | comparison | |
| >= | 2 | R := A >= B; | GreaterThanOrEqual | comparison | |
| < | 2 | R := A < B; | LessThan | comparison | |
| <= | 2 | R := A <= B; | LessThanOrEqual | comparison | |
| <> | 2 | R := A <> B; | NotEqual | comparison |
–jeroen
