catch behavior unclear

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#catch behavior unclear

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kaxori 03/30/2024 01:56 PM

when using a catch, I get exception:

kaxori 03/30/2024 01:57 PM

CODE_INVOCATION_FAILED
Called block with too few arguments.
Got: 0 Expected: 1.
Target:
     testList.<block>.<block>  test.toit:32:24

kaxori 03/30/2024 02:01 PM

I want to catch OUT_OF_BOUNDS EXCEPTION error.
But I get exceptions with valid indices.
What is wrong here ?

bitphlipphar 03/30/2024 02:33 PM

When you use catch:, you're passing a block to the called method. That block is called without any arguments, so if the block you provide expects one or more arguments, you'll get an exception.

bitphlipphar 03/30/2024 02:33 PM

Your block can take arguments in two ways.

bitphlipphar 03/30/2024 02:33 PM

One is explicit: catch: | x y | ....

bitphlipphar 03/30/2024 02:34 PM

Here your block expects two arguments, so it will not work.

kaxori 03/30/2024 02:34 PM

testList:
  DATA ::= [1,2]


  2.repeat:         // works 
    d := DATA[it]
    print "$it: $d"

  2.repeat:
    d := null 
    e := catch --trace : d = DATA[it]
    print "$it: $d"

bitphlipphar 03/30/2024 02:34 PM

The other and more subtle one is the implicit one introduced when the block uses it.

bitphlipphar 03/30/2024 02:35 PM

So here you want the outer block to take an argument, but not the inner one.

bitphlipphar 03/30/2024 02:36 PM

2.repeat: | index | catch --trace: DATA[index]

bitphlipphar

When you use catch:, you're passing a block to the called method. That block is called without any arguments, so if the block you provide expects one or more arguments, you'll ge...

kaxori 03/30/2024 02:43 PM

Thank you:
I'm starting to understand it ...

kaxori 03/30/2024 02:45 PM

... and it already works !

bitphlipphar

The other and more subtle one is the implicit one introduced when the block uses it.

kaxori 03/30/2024 02:54 PM

... so i had a problem with the right use of 'it' ?

kaxori 03/30/2024 02:55 PM

main:
  testList

testList:
  DATA ::= [1,2]

  // force out of bounds error - but catch it
  3.repeat: | index |
    d := null 
    e := catch : d = DATA[index]
    print "$index: $d"

Now it works - as expected !

Nevertheless, what is the difference in using 'it' and 'index' ?(edited)

bitphlipphar 03/30/2024 03:23 PM

Using it, adds an implicitly defined parameter to the innermost block. In your case that was the block passed to catch:.

bitphlipphar 03/30/2024 03:24 PM

After your change, you no longer use it from within the block passed to catch:, so it doesn't get the unwanted parameter.

bitphlipphar 03/30/2024 03:26 PM

When you use index or any other name you explicitly give your block parameters, you do not get any implicitly defined parameters for the block passed to catch:. Instead, the compiler knows that index refers to the parameter in the block passed to repeat:.

kaxori 03/30/2024 03:30 PM

aha : from now on I will avoid 'it' and use only explicit parameters

bitphlipphar 03/30/2024 03:35 PM

I mostly use it for "small" blocks. That's where it really shines.(edited)

20 messages in total