Most REPLs I've used don't print out the output of assignment expressions like a = 1. Being able to suppress this output is very useful when you have a string which is essentially a blob, an object with a large string representation, or even an array of several objects like this. This happens to me often with rails' ActiveRecords where a query might return hundreds of objects that I just want to assign to a variable and don't want to inspect yet. It's even worse with rails because queries are run lazily, just because I did a = User.where(name='Sally') doesn't mean I actually wanted to execute that query against the db yet. I might want to do a = a.where('age > 35'). But irb doing the echo forces the evaluation.
I wrote this patch to irb: https://github.com/ruby/irb/pull/12 which would suppress irb's echo for assignment expressions when a new config setting: context.echo_on_assignment is false. It uses the new RubyVM::AbstractSyntaxTree to determine whether an expression is an assignment expression, so it only works on ruby >= 2.6.0. I'd very much welcome some feedback and any ideas on how to get it to work for earlier ruby versions.
I had also written a first-pass proof-of-concept that used the parser gem and would work for ruby >= 2.0.0 (https://github.com/ruby/irb/pull/11). This version obviously can't be merged because of the external dependency, but perhaps it can be treated like readline: use it if it's already installed, but don't depend on it?
While I use a similar approach suggested by Alan Wu - and there is nothing wrong with that - I think
it may still be useful to have a simpler toggle-way for silencing output by default (or, via a toggle).
I don't know if the original suggestion is good as is, but I think it is an interesting idea to support
(unless there is already some config option for irb that does this, but I am not aware of it).
I don't think an external dependency can be merged, though. For enabling additional functionality,
as suggested by readline, I guess this has to be decided by the ruby core team whether that approach
is good; the better approach would obviously be to have this a possibility for everyone. Perhaps
there is another way to find out whether something is an assignment expression - that could actually
be helpful in general. There are a few ruby projects that have to parse input and find out whether
it is valid ruby syntax or not; and then also determine what this token is doing. I have had a similar
need to do so in one project that aimed to write a shell-wrapper for ruby (and then re-use it in
e. g. ruby bindings to vte, or just as a long loop {} to continually use readline to fetch input,
and act on that input).
So from this point of view I think this may be a useful suggestion.
I don't know if the original suggestion is good as is, but I think it is an interesting idea to support
(unless there is already some config option for irb that does this, but I am not aware of it).
The only option is @context.echo which turns all echo-ing on or off.
I don't think an external dependency can be merged, though.
Yes. As mentioned, that version with the parser gem was just my first-pass proof-of-concept to show what could be done. The first link I gave (https://github.com/ruby/irb/pull/12) has no external dependencies, but it's only available for >= 2.6.0.
Perhaps
there is another way to find out whether something is an assignment expression - that could actually
be helpful in general.
That's exactly what I'm hoping the PR and this feature suggestion would help me find out.
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