R: Create S4 class definition based on XML node(s)

makeClassTemplate {XML} | R Documentation

## Create S4 class definition based on XML node(s)

### Description

This function is used to create an S4 class definition by examining an XML node and mapping the sub-elements to S4 classes. This works very simply with child nodes being mapped to other S4 classes that are defined recursively in the same manner. Simple text elements are mapped to a generic character string. Types can be mapped to more specific types (e.g. boolean, Date, integer) by the caller (via the `types`) parameter. The function also generates a coercion method from an `XMLAbstractNode` to an instance of this new class.

This function can either return the code that defines the class or it can define the new class in the R session.

### Usage

    makeClassTemplate(xnode, types = character(), default = "ANY",
                       className = xmlName(xnode), where = globalenv())

### Arguments

`xnode` | the XML node to analyze
`types` | a character vector mapping XML elements to R classes
`default` | the default class to map an element to
`className` | the name of the new top-level class to be defined. This is the name of the XML node (without the name space)
`where` | typically either an environment or NULL. This is used to control where the class and coercion method are defined or if `NULL` inhibits the code being evaluated. In this case, the code is returned as strings.

### Value

A list with 4 elements:

`name` | the name of the new class
`slots` | a character vector giving the slot name and type name pairs
`def` | code for defining the class
`coerce` | code for defining the coercion method from an XMLAbstractNode to an instance of the new class

If `where` is not `NULL`, the class and coercion code is actually evaluated and the class and method will be defined in the R session as a side effect.

### Author(s)

Duncan Temple Lang

### See Also

`xmlToS4`

### Examples

    txt = paste0("<doc><part><name>ABC</name><type>XYZ</type>",
                "<cost>3.54</cost><status>available</status></part></doc>")
     doc = xmlParse(txt)

     code = makeClassTemplate(xmlRoot(doc)[[1]], types = c(cost = "numeric"))

     as(xmlRoot(doc)[["part"]], "part")

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