GNAT Coding Style
A Guide for GNAT Developers
GNAT, The GNU Ada 95 Compiler
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being “GNU Free Documentation License”, with the Front-Cover Texts being “GNAT Coding Style” and “A Guide for GNAT Developers” and with no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.
Most of GNAT is written in Ada using a consistent style to ensure readability of the code. This document has been written to help maintain this consistent style, while having a large group of developers work on the compiler.
For the coding style in the C parts of the compiler and run time, see the GNU Coding Guidelines.
This document is structured after the Ada Reference Manual. Those familiar with that document should be able to quickly lookup style rules for particular constructs.
FF) should be used. The normal end-of-line sequence is used, which may be
CR, depending on the host system. An optional
16#1A#) may be present as the last character in the file on hosts using that character as file terminator.
ifstatements, loops, and
casestatements. For exact information on required spacing between lexical elements, see file style.adb.
ALIword which stands for Ada Library Information and is by convention always written in upper-case when used in entity names.
Iis too easily confused with
1in some fonts. Similarly don't use the variable
O, which is too easily mistaken for the number
1_000_000 16#8000_000# 3.14159_26535_89793_23846
Digitsare capitalized when used as attribute_designator.
--followed by two spaces). The only exception to this rule (i.e. one space is tolerated) is when the comment ends with a single space followed by
--. It is also acceptable to have only one space between
--and the start of the comment when the comment is at the end of a line, after some Ada code.
--(unlike the normal rule, which is to use entirely blank lines for separating comment paragraphs). The comment starts at same level of indentation as code it is commenting.
z : Integer; -- Integer value for storing value of z -- -- The previous line was a blank line.
begin -- Comment for the next statement A := 5; -- Comment for the B statement B := 6; end;
My_Identifier := 5; -- First comment Other_Id := 6; -- Second comment
Entity1 : Integer; My_Entity : Integer;
E := A * B**2 + 3 * (C - D);
(A / B) * C
elsekeywords fit on the same line with the condition and the
thenkeyword, then the statement is formatted as follows:
if condition then ... elsif condition then ... else ... end if;
When the above layout is not possible,
then should be aligned
if, and conditions should preferably be split before an
or keyword a follows:
if long_condition_that_has_to_be_split and then continued_on_the_next_line then ... end if;
end if always line up with
if keyword. The preferred location for splitting the line
or. The continuation of a condition is
indented with two spaces or as many as needed to make nesting clear.
As an exception, if conditions are closely related either of the
following is allowed:
if x = lakdsjfhlkashfdlkflkdsalkhfsalkdhflkjdsahf or else x = asldkjhalkdsjfhhfd or else x = asdfadsfadsf then ... end if; if x = lakdsjfhlkashfdlkflkdsalkhfsalkdhflkjdsahf or else x = asldkjhalkdsjfhhfd or else x = asdfadsfadsf then ... end if;
ifstatements are indented two characters:
if this_complex_condition and then that_other_one and then one_last_one then ... end if;
ifblock is preceded and followed by a blank line, except where it begins or ends a sequence_of_statements.
A := 5; if A = 5 then null; end if; A := 6;
casestatements, the extra indentation can be saved by aligning the
whenclauses with the opening
case expression is when condition => ... when condition => ... end case;
whileon one line with the condition and the
for J in S'Range loop ... end loop;
If the condition is too long, split the condition (see “If
statements” above) and align
loop with the
while long_condition_that_has_to_be_split and then continued_on_the_next_line loop ... end loop;
If the loop_statement has an identifier, it is laid out as follows:
Outer : while not condition loop ... end Outer;
endwords are aligned, except when the block_statement is named. There is a blank line before the
Some_Block : declare ... begin ... end Some_Block;
infor parameters, especially in functions:
function Length (S : String) return Integer;
procedure Set_Heading (Source : String; Count : Natural; Pad : Character := Space; Fill : Boolean := True);
In the case of a function, if the entire spec does not fit on one line, then the return may appear after the last parameter, as in:
function Head (Source : String; Count : Natural; Pad : Character := Space) return String;
Or it may appear on its own as a separate line. This form is preferred when putting the return on the same line as the last parameter would result in an overlong line. The return type may optionally be aligned with the types of the parameters (usually we do this aligning if it results only in a small number of extra spaces, and otherwise we don't attempt to align). So two alternative forms for the above spec are:
function Head (Source : String; Count : Natural; Pad : Character := Space) return String; function Head (Source : String; Count : Natural; Pad : Character := Space) return String;
----------------- -- My_Function -- ----------------- procedure My_Function is begin ... end My_Function;
Note that the name in the header is preceded by a single space, not two spaces as for other comments.
beginof the enclosing subprogram, there is a comment line and a blank line:
-- Start of processing for Enclosing_Subprogram begin ... end Enclosing_Subprogram;
package P is ... end P;
with-ed packages, with the context clauses looking like:
with A; use A; with B; use B;
package Entity is type Entity_Kind is ...; ... end Entity;
.adbextension for a body or
.adsfor a spec.
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