我在Ada中遇到了一些泛型问题。鉴于以下示例,gnatmake导致:
g_package.adb:13:33: 'Access attribute not allowed in generic body
g_package.adb:13:33: because access type "t_callback_p" is declared outside generic unit (RM 3.10.2(32))
g_package.adb:13:33: move 'Access to private part, or (Ada 2005) use anonymous access type instead of "t_callback_p"
gnatmake: "g_package.adb" compilation error
假设无法更改外部包,有没有办法解决这个问题?我首先得到了错误消息的原因(编译器不知道通用包的正确类型,但是当传递的函数没有触及泛型的任何部分时,它有点烦人。)< / p>
g_package.adb
with Ada.Text_IO; use Ada.Text_IO;
with external;
package body g_package is
procedure quix (f : String) is
begin
Put_Line ("Does a thing");
end quix;
procedure foo (bar : String) is
begin
Put_Line ("baz" & bar & Boolean'Image(flag));
external.procedure_f (quix'Access);
end foo;
end g_package;
g_package.ads
generic
flag : Boolean;
package g_package is
procedure foo (bar : String);
end g_package;
external.ads
package external is
type t_callback_p is access procedure (s : String);
procedure procedure_f (proc : t_callback_p);
end external;
答案 0 :(得分:5)
您可以(如错误消息中所述)移动&#39;访问包规范的私有部分:
private with external;
generic
flag : Boolean;
package g_package is
procedure foo (bar : String);
private
procedure quix (f : String);
quix_access : constant external.t_callback_p := quix'Access;
end g_package;
并使用身体中的常量:
external.procedure_f (quix_access);
答案 1 :(得分:0)
Ada无法做到这一点。如果您希望不可移植并且正在使用(如图所示)GNAT,则可以使用特定于GNAT的属性'Unrestricted_Access
。