CODEWITHSUNDEEP
ada
Master_T
Master_T

Reputation: 7913

Ada Maps: no visible subprogram matches the specification for "="

I've been using Ada.Containers.Indefinite_Hased_Maps to create my own custom hashed maps, and it worked quite well until I tried to use a vector as the element type. Here is an example of the problematic code:

   package String_Vectors is new Ada.Containers.Vectors(Element_Type => Unbounded_String, Index_Type => Natural);
   subtype String_Vector is String_Vectors.Vector;

   package Positive2StringVector_HashMaps is new Ada.Containers.Indefinite_Hashed_Maps --Compiler fails here
     (Element_Type    => String_Vector,
      Key_Type        => Positive,
      Hash            => Positive_Hash,
      Equivalent_Keys => Positive_Equal);

Basically, I cannot Positive2StringVector_HashMaps package, because the compiler comes up with:

no visible subprogram matches the specification for "="

From what I understand, it isn't finding the equality operator for the String_Vector , am I correct? If I am, what is the proper way of implementing it? And if I'm not, what am I doing wrong??

Upvotes: 1

Views: 1665

Answers (1)

Simon Wright
Simon Wright

Reputation: 25501

You don’t need to implement

function “=“ (L, R : String_Vectors.Vector) return Boolean

yourself, because there already is one in String_Vectors; see ALRM A.18.2(12). So you write

package Positive2StringVector_HashMaps is new Ada.Containers.Indefinite_Hashed_Maps
 (Element_Type    => String_Vector,
  Key_Type        => Positive,
  Hash            => Positive_Hash,
  Equivalent_Keys => Positive_Equal,
  “=“             => String_Vectors.”=");

By the way, is there some reason you used Ada.Containers.Vectors on Unbounded_String rather than Indefinite_Vectors on String? (wanting to change the length of a contained string would count as a Good Reason!)

Upvotes: 4

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