ada - 在 Ada 中返回一个包含一个元素的数组

Question

我正在尝试返回一个只有一个元素的函数的数组。我尝试了几种口味，但仍然找不到它想要我做的事情:

with Ada.Text_IO; use Ada.Text_IO;

procedure Beer_Lists is
    type Beer is (Guinness, PBR, Budweiser);
    type Beer_List is array (Positive range <>) of Beer;

    function Beer_I_Like return Beer_List;

    function Beer_I_Like return Beer_List is
    begin
        -- error: Positional aggregate cannot have one component
        -- error: write instead "Beer_List'First => ..."
        return (Guinness);

        -- error: expected type "Beer_List"
        -- error: found type "Beer"
        -- return Guinness;

        -- error: prefix for "First" attribute must be constrained array
        -- return (Beer_List'First => Guinness);

        -- error: named association cannot follow positional association
        -- error: "=>" expected (positional association cannot followed named association)
        -- return (Beer_List'First => Guinness, Guinness);

        -- error: named association cannot follow positional association
        -- return (Guinness, Beer_List'First => Guinness);

        -- error: prefix of attribute must be a name
        -- error: qualify expression to turn it into a name
        -- return (Guinness)'First => Guinness;

        -- error: prefix for "First" attribute must be contrained array
        -- error: missing ";"
        -- return Beer_List'First => Guinness;
    end Beer_I_Like;
begin
    for B of Beer_I_Like loop
        Put_Line (B'Image);
    end loop;
end Beer_Lists;

Answer 1

出于某种原因(我想是为了避免表达式的歧义，但我没有检查)，在 Ada 中您可以使用 位置聚合 形式 (1, 2, 3) 仅当值的数量大于 1 时(记录也是如此)。

解决方案是显式编写索引(或字段名称)，如 (1 => Guiness)