在同一ASSOCIATE构造中的另一个关联实体中引用一个关联名称 [英] Refering to an associating-name in another associating entity in the same ASSOCIATE construct

问题描述

我很抱歉，我的普通话不是很好，但是以下合法的Fortran 2008版本不是吗?

I appologize if my standardese isn't very good but Isn't the following legal Fortran 2008?

program test
  implicit none

  associate ( a => 6, b => 2*a )
    print*, b
  end associate

end program

我的编译器抱怨 a 没有声明并且没有隐式类型.

My compiler complains about a not being declared and not having an implicit type.

我认为选择器只能是一个表达式或变量，而不能是一个关联名称或涉及一个的表达式.是这样吗?

I think the selector can only be an expression or variable and never be an associate-name or an expression involving one. Is this the case?

推荐答案

这是一个(嵌套的)版本，可以满足您的要求，并且您的版本不符合Fortran标准，

Here is a (nested) version that does what you wish, and your version which does not comply with the Fortran standard,

program test
implicit none
integer a ! note that a has be defined here because it is used as a VARIABLE in the association list below
associate ( a => 6, b => 2*a )
    print*, b
end associate
associate ( a => 6 )
    associate ( b => 2*a )
        print*, b
    end associate
end associate
end program

这是Gfortran编译的程序的输出，

Here is the output of the program compiled by Gfortran,

$gfortran -std=gnu main.f90 -o main
$main
   483386368
          12

根据Fortran标准， associate 构造允许人们将名称与变量或表达式的值相关联，在一个块的持续时间内.这是一般语法，

According to the Fortran standard, the associate construct allows one to associate a name either with a variable or with the value of an expression, for the duration of a block. Here is the general syntax,

[ construct-name: ] associate ( association-list )
    block
end associate [ construct-name ]

因此，我相信您对 associate 构造的使用不符合该标准.基本上，在您的代码中，编译器假定 b =>中的 a .关联列表中的2 * a 表示已在关联构造和列表之外定义的变量 a (与名称 a 相反，在关联列表中定义).

Therefore, I believe your usage of the associate construct does not comply with the standard. Basically, in your code, the compiler assumes that a in b => 2*a in the association list refers to a variable a that has been already defined outside the associate construct and list (as opposed to the name a that is defned in the association list).

就像@HighPerformanceMark所建议的那样，嵌套的 associate 构造(如上面的示例)可以实现您想要的目标.

As @HighPerformanceMark suggested, nested associate constructs like the example above could achieve your desired goal.

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