In previous posts, like, Object Oriented Programming, we talked a bit about objects and variables, but in an abstract way. Now, let's get more specific.
A variable is a name for an object. For example, let's think of a person, Nicole, as an object. Now, Nicole, herself is an object, but the word "Nicole" is a name that refers to Nicole the person. Similarly, we can give names to our objects. These names are called variables. Let's see an example:
( var greeting; greeting = "hello world"; greeting.postln; )
To run this code, copy it into a new window in Supercollider and then double click just inside the opening parenthesis to highlight all of it. Then, click the enter key. (Not the return key.) (see also: this video for help.) If you look in the Post window, it should say, "hello world."
What's going on there? The first word, "var," is short for variable. A variable is a storage location. It's a place to store a piece of data. The contents of data stored may vary, which is why it's called a variable. The second word "greeting" is a name. It is the name of the variables. Here we are declaring to the interpreter that we will have a variable named "greeting." The interpreter is the part of SuperCollider that reads and runs our programs. So, when the interpreter is reading our program and sees the word "greeting" it will know that greeting is a variable that we've declared. Otherwise, it wouldn't know what we were talking about.
All variable names in SuperCollider must start with a lowercase letter and cannot be a reserved word. You cannot have a variable called "var" because var already has a special meaning to the interpreter.
Next we are assigning a value to the variable. greeting gets "hello world". The variable is on the left of the equal sign. It must always be on the left. There can only ever be one thing on the left of an equals sign. That sign is saying, 'hey, take whatever is on the right of this equals sign and store it under the variable name on the left.'
In the last line, we're sending a postln message to the variable. The SuperCollider interpreter sends that message to greeting. greeting is a String. Strings print themselves with the postln message. So because greeting is a String, the contents of greeting, "hello world", print out.
On the left is the variable name, an object. Then is a period. Then is the name of the message. There are a few different coding styles allowable in SuperCollider, but we're going to focus on receiver notation because it is common across many programming languages. That is:
Notice the semi-colons. In Supercollider, all instructions must be separated with a semi-colon. A single instruction can span many lines, so the interpretter needs the semi colon to know when one thing is done and another is starting. Later on, when you're trying to figure out why some program isn't working, you're going to discover a missing semicolon. To be on the safe side, it's good practice to put one at the end of every instruction, as in the example.
- Variables are named bits of memory which can store objects.
- Variables must be declared. Their names must start with lowercase letters
- You can assign data to a variable by putting it alone on the left side of an equals sign.
- We send messages to objects with the notation object.message
- Lines of code must be separated with semicolons
The next chapter will make sounds.