[squeak-dev] enabling read-only literals...

Marcel Taeumel marcel.taeumel at hpi.de
Thu Mar 12 11:14:35 UTC 2020


> So do I have everyone's consent in changing trunk over to read-only literals?  If there are no strenuous complaints by tomorrow noon, PST, I shall effect the change.

+1 :-)

Best,
Marcel
Am 11.03.2020 22:10:56 schrieb Eliot Miranda <eliot.miranda at gmail.com>:
Hi All,

    I'v committed the core support for read-only objects, adapted from Clément's Pharo implementation.  Enabling read-only literals is a very small step from that (three methods modified in the parser, and one method modified in Symbol class).  I would like to do this as soon as possible, but it may break code.  Hence my asking for permission/sending out a warning before hand.  Note that the only code it will break is bad code; code that writes to literals.

With the changes installed doing this:

#(1 2 3) at: 2 put: 'nevermore'


raises a ModificationForbidden exception with the message text "ModificationForbidden:  #(1 2 3) is read-only, hence its field 2 cannot be modified with 'nevermore'"


When we added read-only object support to VisualWorks some of the engineering staff were of the opinion that insulating customers from the change was a necessary thing, and so we implemented a preference to allow automatic mutating of read-only literals so that customers whose code did modify literals could set the preference rather than fix their code.  I *really* don't ant to do this.  It is a lot of complication for little gain; the right fix is just to rewrite the code not to write to literals.  Note that that's as easy as:

#(1 2 3) copy at: 2 put: 'nevermore'; yourself
=>
#(1 'nevermore' 3)

since copies of read-only objects are mutable.

So do I have everyone's consent in changing trunk over to read-only literals?  If there are no strenuous complaints by tomorrow noon, PST, I shall effect the change.

To avoid recompiling (which can produce unbound methods, etc) I shall change literals to be read-only via a pass over all literals and a pass over the Symbol table.  Hence the change should be non-invasive.  If your code (like probably 99.9% of all code in the system) doesn't write to literals you won't notice.

_,,,^..^,,,_

best, Eliot
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