3.6.1 Index Constraints and Discrete Ranges
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An
index_constraint
determines the range of possible values for every index of an array subtype,
and thereby the corresponding array bounds.
Syntax
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3
Name Resolution Rules
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Legality Rules
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Static Semantics
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Dynamic Semantics
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An
index_constraint
is
compatible with an unconstrained array subtype if and only
if the index range defined by each
discrete_range
is compatible (see
3.5) with the corresponding
index subtype.
If any of the
discrete_ranges
defines a null range, any array thus constrained is a
null array,
having no components.
An array value
satisfies
an
index_constraint
if at each index position the array value and the
index_constraint
have the same index bounds.
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46 Even if an array value does not satisfy
the index constraint of an array subtype, Constraint_Error is not raised
on conversion to the array subtype, so long as the length of each dimension
of the array value and the array subtype match. See
4.6.
Examples
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Examples of array
declarations including an index constraint:
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Board : Matrix(1 .. 8, 1 .. 8); --
see 3.6
Rectangle : Matrix(1 .. 20, 1 .. 30);
Inverse : Matrix(1 .. N, 1 .. N); --
N need not be static
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Filter : Bit_Vector(0 .. 31);
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Example of array declaration
with a constrained array subtype:
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My_Schedule : Schedule; -- all arrays of type Schedule have the same bounds
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Example of record
type with a component that is an array:
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type Var_Line(Length : Natural) is
record
Image : String(1 .. Length);
end record;
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Null_Line : Var_Line(0); -- Null_Line.Image is a null array