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with Vstrings;
package Tstring is new Vstrings (1024);  -- This is MAXLINE in misc_defs

-- UNIT: generic package body of VSTRINGS
--
-- FILES: vstring_body.a in publiclib
--        related file is vstring_spec.a in publiclib
--
-- PURPOSE:  An implementation of the abstract data type "variable-length
--           string."
--
-- DESCRIPTION:  This package provides a private type VSTRING.  VSTRING objects
--               are "strings" that have a length between zero and LAST, where
--               LAST is the generic parameter supplied in the package
--               instantiation.
--
--               In addition to the type VSTRING, a subtype and two constants
--               are declared.  The subtype STRINDEX is an index to a VSTRING,
--               The STRINDEX constant FIRST is an index to the first character
--               of the string, and the VSTRING constant NUL is a VSTRING of
--               length zero.  NUL is the default initial value of a VSTRING.
--
--               The following sets of functions, procedures, and operators
--               are provided as operations on the type VSTRING:
--
--               ATTRIBUTE FUNCTIONS:  LEN, MAX, STR, CHAR
--                 The attribute functions return the characteristics of
--                 a VSTRING.
--
--               COMPARISON OPERATORS: "=", "/=", "<", ">", "<=", ">="
--                 The comparison operators are the same as for the predefined
--                 type STRING.
--
--               INPUT/OUTPUT PROCEDURES: GET, GET_LINE, PUT, PUT_LINE
--
--                 The input/output procedures are similar to those for the
--                 predefined type STRING, with the following exceptions:
--
--                   - GET has an optional parameter LENGTH, which indicates
--                     the number of characters to get (default is LAST).
--
--                   - GET_LINE does not have a parameter to return the length
--                     of the string (the LEN function should be used instead).
--
--               EXTRACTION FUNCTIONS: SLICE, SUBSTR, DELETE
--                 The SLICE function returns the slice of a VSTRING between
--                 two indices (equivalent to STR(X)(A .. B)).
--
--                 SUBSTR returns a substring of a VSTRING taken from a given
--                 index and extending a given length.
--
--                 The DELETE function returns the VSTRING which results from
--                 removing the slice between two indices.
--
--               EDITING FUNCTIONS: INSERT, APPEND, REPLACE
--                 The editing functions return the VSTRING which results from
--                 inserting, appending, or replacing at a given index with a
--                 VSTRING, STRING, or CHARACTER.  The index must be in the
--                 current range of the VSTRING; i.e., zero cannot be used.
--
--               CONCATENATION OPERATOR:  "&"
--                 The concatenation operator is the same as for the type
--                 STRING.  It should be used instead of APPEND when the
--                 APPEND would always be after the last character.
--
--               POSITION FUNCTIONS: INDEX, RINDEX
--                 The position functions return an index to the Nth occurrence
--                 of a VSTRING, STRING, or CHARACTER from the front or back
--                 of a VSTRING.  Zero is returned if the search is not
--                 successful.
--
--               CONVERSION FUNCTIONS AND OPERATOR: VSTR, CONVERT, "+"
--                 VSTR converts a STRING or a CHARACTER to a VSTRING.
--
--                 CONVERT is a generic function which can be instantiated to
--                 convert from any given variable-length string to another,
--                 provided the FROM type has a function equivelent to STR
--                 defined for it, and that the TO type has a function equiv-
--                 elent to VSTR defined for it.  This provides a means for
--                 converting between VSTRINGs declared in separate instant-
--                 iations of VSTRINGS.  When instantiating CONVERT for
--                 VSTRINGs, the STR and VSTR functions are implicitly defined,
--                 provided that they have been made visible (by a use clause).
--
--                 Note:  CONVERT is NOT implicitly associated with the type
--                 VSTRING declared in this package (since it would not be a
--                 derivable function (see RM 3.4(11))).
--
--                 Caution:  CONVERT cannot be instantiated directly with the
--                 names VSTR and STR, since the name of the subprogram being
--                 declared would hide the generic parameters with the same
--                 names (see RM 8.3(16)).  CONVERT can be instantiated with
--                 the operator "+", and any instantiation of CONVERT can
--                 subsequently be renamed VSTR or STR.
--
--                 Example:  Given two VSTRINGS instantiations X and Y:
--                   function "+" is new X.CONVERT(X.VSTRING, Y.VSTRING);
--                   function "+" is new X.CONVERT(Y.VSTRING, X.VSTRING);
--
--                   (Y.CONVERT could have been used in place of X.CONVERT)
--
--                   function VSTR(A : X.VSTRING) return Y.VSTRING renames "+";
--                   function VSTR(A : Y.VSTRING) return X.VSTRING renames "+";
--
--                 "+" is equivelent to VSTR.  It is supplied as a short-hand
--                 notation for the function.  The "+" operator cannot immed-
--                 iately follow the "&" operator; use ... & (+ ...) instead.
pragma Page;