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class tag

Persistent logic tag

Defines a custom tag from which multiple instances can be created.

Note: class cannot be used to define transient logic tags.

Sample usage

<heading:class _=text *=<span size=40 bold=true {</p><text:span></p>}>> creates a heading tag that can be used to create consistently sized heading text throughout an app, with a paragraph break before and after the heading text.

<b:class *=<span bold=true>> creates a b tag that can be used to make text bold.

Fields

Primary field

None

Secondary fields

*: (required) sets the tag definition
_: (optional) defines the primary field by providing a path to a field or tag inside the class definition, that the primary tag of an instance will correspond to
Other fields defined by the user: (optional) define other fields for the class by providing paths to their corresponding fields or tags inside the class definition.

Behaviour

Classes provide a way to define your own custom presentation tags (or persistent logic tags in some cases).

To be useful, a class tag must be given a name, like <tagName:class ....>. The tag name can later be used anywhere within the scope of where the tag is defined, to create a new instance of the custom tag type.

A class also requires a tag definition, defined in the * field. This definition must consist of a single presentation or persistent logic tag, which may optionally be given a name of its own. That tag may itself contain as many tags and fields as needed to define the custom tag's appearance and behaviour.

All tag and field names within the definition are internal to the tag definition. They are hidden from the user of that tag. To expose tags and fields to the user, add fields to the class tag, where each field contains the path to the corresponding field inside the tag definition. Set the _ field to define which internal tag or field the custom tag's primary field will correspond to.

If you do not set the _ field, the custom tag's primary field will correspond to the primary field of the main tag inside the tag definition.

Example

The following example creates a heading class, with the heading's text size exposed as a field so that headings of different levels can be created.

<heading:class _=text size=text.size *=
  <span bold=true {</p><text:span size=30 {}></p>}>
>

<heading size=40 {Top level heading}>
<heading size=26 {Sub-heading}>
<heading {Default size}>
Body text

Top level heading Sub-heading Default size Body text

The class defines a span containing an inner span named text. The _ field makes the class's primary field correspond to text, so each heading's text goes there, between two paragraph breaks. The size field is exposed as the size field of text, so it can be given when each heading is created; the definition gives it a default of 30.

Notes

Field values given to an instance are applied after the definition has been carried out. In ioL version 1.05, this means a value calculated inside the definition (for example a size worked out from another exposed field) uses the definition's default rather than the instance's value. Expose the field to be changed directly, as above.

Fields that aren't exposed are hidden from outside the instance, including from code that reaches the instance through a reference pointer.