Sha256: bcb51b82ba25cb678bf054b8f345b7af16a33409680e3dea9a7c2d013493ab42
Contents?: true
Size: 1.51 KB
Versions: 33
Compression:
Stored size: 1.51 KB
Contents
---
layout: post
title: "Instance Variable"
keywords: attr_reader, @, instance
permalink: objects/instance.html
---
A instance variable in ruby has a name beginning with `@`. It often makes sense for it to be initialised at `setup` (not necessarily in the loop could be called method).
```ruby
#!/usr/bin/env jruby -v -W2
require 'picrate'
class Tree < Processing::App
# http://processing.org/learning/topics/tree.html
# by Joe Holt
def setup
size 200, 200
end
def setup
sketch_title 'Tree'
color_mode RGB, 1
frame_rate 30
smooth
@x = 0.0
@dx = width / 100
@start_time = Time.now
@frame_time = nil
end
def draw
t = Time.now
if @frame_time
fps = 1.0 / (t - @frame_time)
# printf "%0.1f fps\n", fps
end
@frame_time = t
# ...etc
Tree.new
```
For a variable that gets called quite a lot in a PiCrate sketch it makes sense to create a getter using `attr_reader`. This has the fortunate side effect of making it blindingly obvious when you are assigning it to a new value/instance (it also makes the sketch variable readable by external classes).
```ruby
#!/usr/bin/env jruby -w
require 'picrate'
class Interpolate < Processing::App
attr_reader :x, :y
def setup
sketch_title 'Interpolate'
@x, @y = 0, 0
no_stroke
end
def draw
background(51)
@x = lerp(x, mouse_x, 0.05)
@y = lerp(y, mouse_y, 0.05)
fill(255)
stroke(255)
ellipse(x, y, 66, 66)
end
def settings
size(640, 360)
end
end
Interpolate.new
```
Version data entries
33 entries across 33 versions & 1 rubygems