On Tue, Jul 23, 2013 at 2:02 AM, St�phane Ducasse <stephane.ducasse@inria.fr> wrote:

thanks!
It makes a lot of sense.
I will play with another example because I want to really understand the outerContext of closure vs the home context.

The outerContext is a link in the static chain. �Each block is created inside some context. �This is the block's outerContext. �If the block is not nested then the outerCOntext will also be the home context �But if the block is nested inside another block activation, then the outerContext refers to that block activation, and the block activation's block's outerContext is the home context. �So there are as many outerContext steps as there are nesting levels.

| homeContext b1 |

homeContext := thisContext.

b1 := [| b2 |

� � � � � self assert: thisContext closure == b1.

� � � � � self assert: b1 outerContext == homeContext.

� � � � � b2 := [self assert: thisContext closure == b2.

� � � � � � � � � � self assert: b2 outerContext closure outerContext == homeContext].

� � � � � b2 value].

b1 value�

Ignore the "bN appears to be undefined at this point" and evaluate the above. �No assert fails.

Draw a picture.

Stef

On Jul 23, 2013, at 6:58 AM, Cl�ment Bera <bera.clement@gmail.com> wrote:

This is because of compilation optimization.

2013/7/22 St�phane Ducasse <stephane.ducasse@inria.fr>

Hi

when I execute the following

first
� � � � "Bexp new first"
� � � � | temp |
� � � � temp := �2.
� � � � [ temp.
� � � � thisContext inspect.] value.
� � � � ^ temp

tmp in the inspector is nil and does not hold 2 and I was wondering why.
I thought that thisContext was returning the blockContext
In the outercontext of thisContext blockClosure, tmp is also nil.

�
This is because here 'temp.' is evaluated for effect (the value is not stored anywhere) and it has no side effect (reading a variable cannot lead to a modification of state of another object). So the compiler removes it. As it is removed, it is the same as if it was not in the block. So the block cannot access temp. Now write 'temp:= #foo' or 'temp foo' you will get it.

�
first
� � � � "Bexp new first"
� � � � | temp |
� � � � temp := �2.
� � � � [ temp.
� � � � temp traceCr.
� � � � thisContext inspect.] value.
� � � � ^ temp

output 2 on the transcript.

In this case 'temp.' is still removed, but the value of temp still need to be copied in the block for '�temp traceCr.'.'temp traceCr' is also evaluated for effect, but has the side effect to output the transcript, so the compiler cannot remove it.

Basically the is very few things that the compiler removes, and one of them is variable read for effect, because you are sure it cannot lead to any issue.
�
Stef