4.5.2 Relational Operators and Membership Tests
= (equals) and /= (not equals) are predefined
for nonlimited types.
are the ordering operators
< (less than), <= (less than
or equal), > (greater than), and >= (greater than or equal).
ordering operators are predefined for scalar types, and for discrete
, that is, one-dimensional array types whose components
are of a discrete type.
, using in
or not in
whether or not a value belongs to a given subtype or range, or has a
tag that identifies a type that is covered by a given type. Membership
tests are allowed for all types.
Name Resolution Rules
of a membership test is the type of the range
or the type determined by the subtype_mark
If the tested type is tagged, then the simple_expression
shall resolve to be of a type that is convertible (see 4.6
to the tested type; if untagged, the expected type for the simple_expression
is the tested type.
For a membership test, if the simple_expression
is of a tagged class-wide type, then the tested type shall be (visibly)
The result type of a membership test is the predefined
The equality operators
are predefined for every specific type T that is not limited,
and not an anonymous access type, with the following specifications:
function "=" (Left, Right : T) return Boolean
function "/="(Left, Right : T) return Boolean
The following additional
equality operators for the universal_access type are declared
in package Standard for use with anonymous access types:
function "=" (Left, Right : universal_access) return Boolean
function "/="(Left, Right : universal_access) return Boolean
The ordering operators
are predefined for every specific scalar type T, and for every
discrete array type T, with the following specifications:
function "<" (Left, Right : T) return Boolean
function "<="(Left, Right : T) return Boolean
function ">" (Left, Right : T) return Boolean
function ">="(Left, Right : T) return Boolean
Name Resolution Rules
At least one of the
operands of an equality operator for universal_access
of a specific anonymous access type. Unless the predefined equality operator
is identified using an expanded name with prefix
denoting the package Standard, neither operand shall be of an access-to-object
type whose designated type is D
'Class, where D
has a user-defined primitive equality operator such that:
- its result type is Boolean;
- it is declared immediately within
the same declaration list as D; and
- at least one of its operands is an
access parameter with designated type D.
At least one of the operands of the equality operators
for universal_access shall be of type universal_access,
or both shall be of access-to-object types, or both shall be of access-to-subprogram
- When both are of access-to-object
types, the designated types shall be the same or one shall cover the
other, and if the designated types are elementary or array types, then
the designated subtypes shall statically match;
- When both are of access-to-subprogram
types, the designated profiles shall be subtype conformant.
For discrete types, the predefined relational operators
are defined in terms of corresponding mathematical operations on the
position numbers of the values of the operands.
For real types, the predefined relational operators
are defined in terms of the corresponding mathematical operations on
the values of the operands, subject to the accuracy of the type.
Two access-to-object values are equal if they designate
the same object, or if both are equal to the null value of the access
Two access-to-subprogram values are equal if they
are the result of the same evaluation of an Access attribute_reference
or if both are equal to the null value of the access type. Two access-to-subprogram
values are unequal if they designate different subprograms.
is unspecified whether two access values that designate the same subprogram
but are the result of distinct evaluations of Access attribute_reference
are equal or unequal.
For a type extension, predefined
equality is defined in terms of the primitive (possibly user-defined)
equals operator of the parent type and of any tagged components of the
extension part, and predefined equality for any other components not
inherited from the parent type.
For a private type, if its full type is tagged, predefined
equality is defined in terms of the primitive equals operator of the
full type; if the full type is untagged, predefined equality for the
private type is that of its full type.
other composite types, the predefined equality operators (and certain
other predefined operations on composite types — see 4.5.1
) are defined in terms of the corresponding
operation on matching components
, defined as follows:
- For two one-dimensional arrays of
the same type, matching components are those (if any) whose index values
match in the following sense: the lower bounds of the index ranges are
defined to match, and the successors of matching indices are defined
- For two multidimensional arrays of
the same type, matching components are those whose index values match
in successive index positions.
The analogous definitions apply if the types of the
two objects or values are convertible, rather than being the same.
Given the above definition
of matching components, the result of the predefined equals operator
for composite types (other than for those composite types covered earlier)
is defined as follows:
- If there are no components, the result
is defined to be True;
- If there are unmatched components,
the result is defined to be False;
- Otherwise, the result is defined in
terms of the primitive equals operator for any matching tagged components,
and the predefined equals for any matching untagged components.
For any composite type, the order in which "="
is called for components is unspecified. Furthermore, if the result can
be determined before calling "=" on some components, it is
unspecified whether "=" is called on those components.
The predefined "/=" operator gives the
complementary result to the predefined "=" operator.
For a discrete array type, the
predefined ordering operators correspond to lexicographic order
using the predefined order relation of the component type: A null array
is lexicographically less than any array having at least one component.
In the case of nonnull arrays, the left operand is lexicographically
less than the right operand if the first component of the left operand
is less than that of the right; otherwise the left operand is lexicographically
less than the right operand only if their first components are equal
and the tail of the left operand is lexicographically less than that
of the right (the tail
consists of the remaining components beyond
the first and can be null).
For the evaluation of a membership
test, the simple_expression
and the range
(if any) are evaluated in an arbitrary order.
A membership test using
in yields the result True if:
- The tested type is scalar, and the
value of the simple_expression
belongs to the given range,
or the range of the named subtype; or
tested type is not scalar, and the value of the simple_expression
satisfies any constraints of the named subtype, and:
- if the type of the simple_expression
is class-wide, the value has a tag that identifies a type covered by
the tested type;
- if the tested type is an access
type and the named subtype excludes null, the value of the simple_expression
is not null.
Otherwise the test yields the result False.
A membership test using not in gives the complementary
result to the corresponding membership test using in.
For all nonlimited types declared in language-defined
packages, the "=" and "/=" operators of the type
shall behave as if they were the predefined equality operators for the
purposes of the equality of composite types and generic formal types.
This paragraph was
13 If a composite type has components that
depend on discriminants, two values of this type have matching components
if and only if their discriminants are equal. Two nonnull arrays have
matching components if and only if the length of each dimension is the
same for both.
Examples of expressions
involving relational operators and membership tests:
X /= Y
"" < "A" and "A" < "Aa" -- True
"Aa" < "B" and "A" < "A " -- True
My_Car = null
-- true if My_Car has been set to null (see 3.10.1)
My_Car = Your_Car -- true if we both share the same car
-- true if the two cars are identical
N not in
1 .. 10 -- range membership test
Mon .. Fri -- range membership test
Weekday -- subtype membership test (see 3.5.1)
Disk_Unit -- subtype membership test (see 3.8.1)
Addition'Class -- class membership test (see 3.9.1)