Jira (PUP-5927) Add default value to Optional type

[Henrik Lindberg (JIRA)]

Title: Message Title

Henrik Lindberg created an issue   Puppet / PUP-5927 Add default value to Optional type Issue Type: New Feature Assignee: Unassigned Created: 2016/02/19 7:22 AM Fix Versions: PUP 4.x Priority: Normal Reporter: Henrik Lindberg It is of value to let an Optional define a default value (to be used when no value was given). This centralises the control over what the default value should be - without this, every place that optional type is used the user needs to set the same default value using a default value _expression_. The syntax is: Optional[T, <default_value>] There is one quirk in making this work in a backwards compatible way. Users that are now using Optional has no expectancy that it can define a default value. Therefore, when not stating the default value for an Optional, it must behave exactly as it does now. If no default value is given, a default literal value is set as the optional's default value If the optional's default value is a default literal it means the Optional has the same behaviour as it has now. The default value must be a value that is assignable to T (or the literal default). The rationale for these rules are that it is of value to be able to have an undef default value. Users rarely (if ever) wants to use the special literal default as a default value. At runtime when matching parameters, the following rules applies: If user gives a value - this value wins unless the value is undef and the target is a class or definition parameter in which case the given undef has the same outcome as if user did not give a value. If user gave no value (or special case above applies) If data binding returns a value other than undef, this value wins If data binding returns undef: then this undef wins iff there is no default value _expression_ for the parameter, and the parameter's Optional type has no default value. else if there is a default value _expression_ for the parameter it wins if the parameter's Optional type has a default value it wins If the parameter's type is a complex type including Optional types and they unambiguously defines a default value, then this default value wins. If a complex parameter type is used and there is a default value ambiguity, an error is raised "default value specified by multiple Optional types, use a default value _expression_ for the parameter to resolve this ambiguity". Add Comment   This message was sent by Atlassian JIRA (v6.4.12#64027-sha1:e3691cc) -- You received this message because you are subscribed to the Google Groups "Puppet Bugs" group. To unsubscribe from this group and stop receiving emails from it, send an email to puppet-bugs+unsubscr...@googlegroups.com. To post to this group, send email to puppet-bugs@googlegroups.com. Visit this group at https://groups.google.com/group/puppet-bugs. For more options, visit https://groups.google.com/d/optout.