Книга: Standard Template Library Programmer
Strict Weak Ordering
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Strict Weak Ordering
Category: functors
Component type: concept
Description
A Strict Weak Ordering is a Binary Predicate that compares two objects, returning true if the first precedes the second. This predicate must satisfy the standard mathematical definition of a strict weak ordering. The precise requirements are stated below, but what they roughly mean is that a Strict Weak Ordering has to behave the way that "less than" behaves: if a is less than b then b is not less than a, if a is less than b and b is less than c then a is less than c, and so on.
Refinement of
Binary Predicate
Associated types
| First argument type | The type of the Strict Weak Ordering's first argument. |
| Second argument type | The type of the Strict Weak Ordering's second argument. The first argument type and second argument type must be the same. |
| Result type | The type returned when the Strict Weak Ordering is called. The result type must be convertible to bool. |
Notation
F A type that is a model of Strict Weak Ordering
X The type of Strict Weak Ordering's arguments.
f Object of type F
x, y, z Object of type X
Definitions
• Two objects x and y are equivalent if both f(x, y) and f(y, x) are false. Note that an object is always (by the irreflexivity invariant) equivalent to itself.
Valid expressions
None, except for those defined in the Binary Predicate requirements.
Expression semantics
| Name | Expression | Precondition | Semantics | Postcondition |
|---|---|---|---|---|
| Function call | f(x, y) |
The ordered pair (x,y) is in the domain of f | Returns true if x precedes y, and false otherwise | The result is either true or false |
Invariants
| Irreflexivity | f(x, x) must be false. |
| Antisymmetry | f(x, y) implies !f(y, x) |
| Transitivity | f(x, y) and f(y, z) imply f(x, z). |
| Transitivity of equivalence | Equivalence (as defined above) is transitive: if x is equivalent to y and y is equivalent to z, then x is equivalent to z. (This implies that equivalence does in fact satisfy the mathematical definition of an equivalence relation.) [1] |
Models
• less<int>
• less<double>
• greater<int>
• greater<double>
Notes
[1] The first three axioms, irreflexivity, antisymmetry, and transitivity, are the definition of a partial ordering; transitivity of equivalence is required by the definition of a strict weak ordering. A total ordering is one that satisfies an even stronger condition: equivalence must be the same as equality.
See also
LessThan Comparable, less, Binary Predicate, function objects
Оглавление книги
- Restricting Access with allow and deny
- Miscellaneous Tweaks
- 6.3.1. Strict Consistency
- 6.3.5. Weak Consistency
- Restricting call times
- Restricting NNTP Access
- Allowing and restricting zone transfers
- Configuring point and print restrictions
- 6.16.10 Кодирование Strict Source Route
- 5.7.3. "use strict"
- Breakpoint Restrictions
- Строгий режим (strict mode)