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A.10.10 Input-Output for Enumeration Types

Static Semantics

The following procedures are defined in the generic package Enumeration_IO, which has to be instantiated for the appropriate enumeration type (indicated by Enum in the specification).

Values are output using either upper or lower case letters for identifiers. This is specified by the parameter Set, which is of the enumeration type Type_Set.

   
       type Type_Set is (Lower_Case, Upper_Case);

The format (which includes any trailing spaces) can be specified by an optional field width parameter. The default field width and letter case are defined by the following variables that are declared in the generic package Enumeration_IO:

   
       Default_Width   : Field := 0;
       Default_Setting : Type_Set := Upper_Case;

The following procedures are provided:

   
       procedure Get(File : in File_Type; Item : out Enum);
       procedure Get(Item : out Enum);

After skipping any leading blanks, line terminators, or page terminators, reads an identifier according to the syntax of this lexical element (lower and upper case being considered equivalent), or a character literal according to the syntax of this lexical element (including the apostrophes). Returns, in the parameter Item, the value of type Enum that corresponds to the sequence input.

The exception Data_Error is propagated if the sequence input does not have the required syntax, or if the identifier or character literal does not correspond to a value of the subtype Enum.

    
       procedure Put(File  : in File_Type;
                     Item  : in Enum;
                     Width : in Field := Default_Width;
                     Set   : in Type_Set := Default_Setting);

       procedure Put(Item  : in Enum;
                     Width : in Field := Default_Width;
                     Set   : in Type_Set := Default_Setting);

Outputs the value of the parameter Item as an enumeration literal (either an identifier or a character literal). The optional parameter Set indicates whether lower case or upper case is used for identifiers; it has no effect for character literals. If the sequence of characters produced has fewer than Width characters, then trailing spaces are finally output to make up the difference. If Enum is a character type, the sequence of characters produced is as for Enum'Image(Item), as modified by the Width and Set parameters.

    
       procedure Get(From : in String; Item : out Enum; Last : out Positive);

Reads an enumeration value from the beginning of the given string, following the same rule as the Get procedure that reads an enumeration value from a file, but treating the end of the string as a file terminator. Returns, in the parameter Item, the value of type Enum that corresponds to the sequence input. Returns in Last the index value such that From(Last) is the last character read.

The exception Data_Error is propagated if the sequence input does not have the required syntax, or if the identifier or character literal does not correspond to a value of the subtype Enum.

    
       procedure Put(To   : out String;
                     Item : in Enum;
                     Set  : in Type_Set := Default_Setting);

Outputs the value of the parameter Item to the given string, following the same rule as for output to a file, using the length of the given string as the value for Width.

Although the specification of the generic package Enumeration_IO would allow instantiation for an float type, this is not the intended purpose of this generic package, and the effect of such instantiations is not defined by the language.

NOTES

(32) There is a difference between Put defined for characters, and for enumeration values. Thus

    
          Ada.Text_IO.Put('A');  --  outputs the character A

          package Char_IO is new Ada.Text_IO.Enumeration_IO(Character);
          Char_IO.Put('A');  --  outputs the character 'A', between apostrophes

(33) The type Boolean is an enumeration type, hence Enumeration_IO can be instantiated for this type.

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