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0 pointsxen02y ago0 comments

I don't think that helps?

If, as is kind of the point of RAII, your constructors do some initialization and that initialization may fail, then:

If you have a single object that may fail to construct then maintaining it in scope for the catch block doesn't make sense; it's not initialized.

If you have several, then you still can't maintain them in scope, because you don't know which ones are actually valid.

Yes there are other patterns that wouldn't have this issue (acquiring resources outside of the constructor), but then you can just declare your objects outside of the try-catch block.

0 pointsxen02y ago0 comments

I don't think that helps?

If, as is kind of the point of RAII, your constructors do some initialization and that initialization may fail, then:

If you have a single object that may fail to construct then maintaining it in scope for the catch block doesn't make sense; it's not initialized.

If you have several, then you still can't maintain them in scope, because you don't know which ones are actually valid.

Yes there are other patterns that wouldn't have this issue (acquiring resources outside of the constructor), but then you can just declare your objects outside of the try-catch block.

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5 comments · 1 top-level

specialist2y ago· 4 in thread

I misspoke.

Ignoring the syntax for a moment, I want scoping to behave like this pseudo-code. So that the catch and finally blocks are lexically nested within the parent try block.

  try {

    OutputStream out = ...

    ...

  // Must be at end of try block
  catch ExceptionA, Exception B { ... }

  catch Exception C { ... }

  finally { ... }
    

  } // end of try

Maybe even allow catch and finally to allow single expression in addition to blocks. Just like with if/then/else.

xen0OP2y ago

Right, but if constructing OutputStream throws ExceptionA, you shouldn't have it in scope; it's not something you can use.

specialist2y ago

Agreed. I'll make that more clear next time. I omitted catch's parens, which makes it less clear.

I just want 'out' visible to both catch and finally.

nemetroid2y ago

If constructing "out" fails but one of the catch-blocks tries to use "out", what should happen?

grumbel2y ago

Python is an example of a language that works like this. When the constructor throws, 'out' remains not defined, but you can just do 'out = ...' in the catch block and define one with a fallback value. So all the code after the error handing would just see a working 'out' variable. This works due to all variables being bound to the function scope, not to the code block, in Python.

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