Ada 2012 RM - 注释和字符串文字

Question

我正在浏览 Ada 2012 RM，想看看我的理解是否有漏洞或 RM 是否存在漏洞。假设

    put_line ("-- this is a not a comment");

是合法的代码，我怎么能从 RM 中推断出它的合法性，因为第 2.7 节指出 "a comment starts with two adjacent hyphens and extends up to the end of the line."，而第 2.6 节指出“string_literal 是由一系列图形字符组成的（可能 none) 包含在两个之间用作字符串括号的引号。”这两个部分之间似乎存在紧张关系，2.7 会获胜，但显然并非如此。

Answer 1

为了更清楚地了解这里，您需要查看 RM 中的第 2.2 节。

2.2 (1)，其中规定；

The text of each compilation is a sequence of separate lexical elements. Each lexical element is formed from a sequence of characters, and is either a delimiter, an identifier, a reserved word, a numeric_literal, a character_literal, a string_literal, or a comment. The meaning of a program depends only on the particular sequences of lexical elements that form its compilations, excluding comments.

和 2.2 (3/2) 其中指出：

"[In some cases an explicit separator is required to separate adjacent lexical elements.] A separator is any of a separator_space space character, a format_effector format effector, or the end of a line, as follows:

A separator_space space character is a separator except within a comment, a string_literal, or a character_literal.

The character whose code point position is 16#09# (CHARACTER TABULATION) Character tabulation (HT) is a separator except within a comment.

The end of a line is always a separator.

One or more separators are allowed between any two adjacent lexical elements, before the first of each compilation, or after the last."

和

A delimiter is either one of the following special characters:

&    '    (    )    *    +    ,    –    .    /    :    ;    <    =    >    |

or one of the following compound delimiters each composed of two adjacent special characters

=>    ..    **    :=    /=    >=    <=    <<    >>    <>

Each of the special characters listed for single character delimiters is a single delimiter except if this character is used as a character of a compound delimiter, or as a character of a comment, string_literal, character_literal, or numeric_literal.

所以，一旦你过滤掉程序文本的白色-space并将其分解为一系列词法元素，则字符串文字对应的词法元素以双引号字符开头，并且对应于注释的词汇元素以 --.

开头

这些是明显不同的语法项，彼此不冲突。

这也解释了为什么；

X := A - -1
      + B;

给出的结果不同于；

X := A --1
       + B;

破折号之间的 space 分隔符使第一个减号成为与 -1 不同的词法元素，因此 -1 在第一种情况下是数字文字，而 --1 是注释。

Ada 2012 RM - 注释和字符串文字

Ada 2012 RM - Comments and String Literals

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