Getting properties by using reflection

The type.TypeInfo object includes a property called Properties, which contains a list of type properties. Each item in that list includes metadata properties such as the name (Name) and a short description (ShortDescription).

Because of performance implications and the inability to find errors at compile time, only use reflection if there is no other way to do what you need.

To examine how reflection provides information about class properties, paste the following code into the Gosu Scratchpad.

var object = "This is a string"
var propNames = ""
var props = (typeof object).TypeInfo.Properties

for (prop in props) {
  propNames = propNames + prop.Name + "  "
}

print(propNames)

This code prints lines similar to the following output.

Class  Bytes  Empty  CASE_INSENSITIVE_ORDER  Digits  AsBigDecimal  length  size  HasContent
NotBlank  Alpha  AlphaSpace  Alphanumeric  AlphanumericSpace  Numeric  NumericSpace  Whitespace

Array syntax for getting a property by using reflection

Gosu also provides a concise associative array syntax to access properties by reflection. This syntax uses square brackets to access properties, similar to using arrays. The property name is case sensitive.

Note: The [] operator applies to all objects and has the typical meaning for List, Array, and Map objects. For other objects, the [] syntax performs a reflective look-up.

For example, paste the following code into the Gosu Scratchpad.

var dateObject = new Date()
var propertyName = "Hour"

// Get a property name using reflection
print(dateObject[propertyName])

If the time is currently 5:00 a.m., this code prints the following output.

Consider the following Gosu class:

public class ObjClass {
  property get MyProperty() : String {
    return "Default value for MyProperty"
  }
}

The following code declares an object of class ObjClass and uses array syntax to access the MyProperty property by reflection:

var obj = new ObjClass()
var val = obj["MyProperty"]

This code is equivalent to the following:

var obj = new ObjClass()
var val = (typeof obj).TypeInfo.getProperty("MyProperty").Accessor.getValue(obj)