Ada Programming/Keywords/aliased
Description
editIf you come from C/C++ you are probably used to the fact that every element of an array, struct/record and other variables has an address. The C/C++ standards actually demand that. In Ada this is not true.
Ada is a self optimizing language — there is for example no register keyword like in C/C++. Ada compilers will use a register for storage automatically. Incidentally, most C/C++ compilers nowadays just ignore the register and allocate registers themselves, just like Ada does.
So if you want to take an access from any variable you need to tell the compiler that the variable needs to be in memory and may not reside inside a register. This is what the keyword aliased is for. Additionally it also serves as a hint to the reader of the program about the existence of pointers referencing the variable.
For variables
editI : aliased Integer := 0;
For type declarations
editFor the elements of an array
editDeclaring an array as aliased will only ensure that the array as a whole has an address. It says nothing about the individual elements of the array — which may be packed in a way that more than one element has the same address. You need to declare the actual elements as aliased as well. You can read in Types/array how this is done. Here is just a short example:
typeDay_Of_Monthisrange1 .. 31;typeDay_Has_Appointmentisarray(Day_Of_Month)ofaliasedBoolean;
For the elements of a record
editJust like arrays, declaring a record as aliased will only ensure that the record as a whole has an address. It says nothing about the individual elements of the record — which again may be packed and share addresses. Again you need to declare the actual elements as aliased as well. You can read in Types/record how this is done. Here is just a short example:
typeBasic_RecordisrecordA :aliasedInteger;endrecord;
See also
editWikibook
editAda Reference Manual
editAda Quality and Style Guide
edit
| Ada Keywords | ||||
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abort
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else
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new
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return
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abs
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elsif
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not
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reverse
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abstract (Ada 95)
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end
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null
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accept
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entry
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select
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access
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exception
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of
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separate
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aliased (Ada 95)
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exit
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or
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some (Ada 2012)
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all
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others
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subtype
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and
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for
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out
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synchronized (Ada 2005)
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array
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function
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overriding (Ada 2005)
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at
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tagged (Ada 95)
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generic
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package
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task
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begin
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goto
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parallel (Ada 2022)
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terminate
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body
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pragma
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then
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if
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private
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type
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case
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in
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procedure
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constant
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interface (Ada 2005)
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protected (Ada 95)
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until (Ada 95)
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is
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use
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declare
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raise
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delay
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limited
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range
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when
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delta
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loop
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record
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while
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digits
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rem
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with
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do
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mod
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renames
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requeue (Ada 95)
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xor
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