Re: [Pharo-users] Is it possible to follow an object through a computation?

[Steven Costiou via Pharo-users]

--- Begin Message ---

Hi, 

if you are using Pharo 7 I have some work on object-centric debugging
that could do that, using Reflectivity. 

For example, with object-centric metalinks you could do the following: 

##get your object (here are two instances of a trivial class which only
has a "name" inst var) 

obj1 := MyClass new.
obj2 := MyClass new. 

##define a "halt" metalink: 

link := MetaLink new 
    metaObject: Halt; 
    selector: #now;
    control: #before.    

##install the metalink on the  instance variable "name" of the  first
object using the new Reflectivity API 

obj1 link: link toSlotNamed: #name. 

##then the system only halts when you use a method accessing the "name"
slot of this object, and not for other instances 

obj1 name: 'first name'. <-- halt
obj2 name: 'second name' <-- no halt 

If you look at Object and Class classes, you will find a more detailed
API to install metalinks on different structural entities and to scope
them to objects. For example you can ask to halt only when a instance
variable is read, or only when something is written in it (in the
example above it does both). 

These metalinks are only available for Pharo 7 and must be loaded from
https://github.com/StevenCostiou/Reflectivity-dev and you must override
the current Reflectivity code (click "load" and not "merge"). Hopefully
that will be integrated and merged in Pharo 7 or 8 soon. 

There is also that https://github.com/ClotildeToullec/Collectors/wiki
which provides a history tool that stores all objects that went into an
instance variable of an object (or even a temp var or a given
expression). It uses the Reflectivity API mentionned above. However for
now it is needed to provide a condition to scope the capture of objects
to a specific instance (but it works well). This tool also gives you the
stack for each modification of an instance variable. Objects are stored
in memory though, so it can kill your image on too large program
executions (that part is currently being investigated...). 

I do not have time right now to get into more details, but if you try
any of it and have questions please ask. 

Steven. 

  

--- End Message ---