The trigger gets fired whenever a value is explicitly set for an attribute, but not when it's implicitly set by a default/builder. Basically, it's triggered by the outside world setting a value, but not triggered by the internal workings of the attribute. The default/builder is itself a coderef though, so can execute arbitrary code, including doing whatever the trigger would do.

I don't think this violates the principle of least surprise if you consider the usual definition of "trigger". A trigger is a device that responds when it is pressed. You press the trigger on an attribute by supplying a value for it. If you don't supply a value for it, then the trigger doesn't get pressed.

In any case, Moose has had this behaviour for triggers since they were introduced in 2006, and changing it would break a lot of stuff.

toby döt ink

In reply to Re^5: Types::DateTime, DateTimeUTC->plus_coercions( Format['ISO8601'] ), output format override question by tobyink
in thread Types::DateTime, DateTimeUTC->plus_coercions( Format['ISO8601'] ), output format override question by Your Mother

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.