The Warehouse Metaphor
Think of memory as a giant warehouse.
Like this warehouse from the movie Raiders of the Lost Ark, computer memory is vast and filled with boxes of various sizes.
A VARIABLE is a NAME for an object. You give an object a name using the ASSIGNMENT operator (it looks like an equal sign).
color = "blue"
fruit = "berry"
Anywhere you can use an object, you can use a variable instead.
color + fruit
fruit.upcase
Think of memory as a giant warehouse.
Like this warehouse from the movie Raiders of the Lost Ark, computer memory is vast and filled with boxes of various sizes.
If memory is a giant warehouse...
...and objects are boxes in that warehouse
...then a value is the contents of a box
...and a variable is a label you stick on the outside of the box
Which is clearer, this:
60 * 60 * 24
or this:
seconds_per_minute = 60
minutes_per_hour = 60
hours_per_day = 24
seconds_per_day = seconds_per_minute * minutes_per_hour * hours_per_day
?
Let's spend a few minutes just playing around in IRB. Some things to try:
snack = "Apple"
Think of a variable as pointing to an object.
You can assign and reassign variables at will.
color = "blue"
fruit = "berry"
color + fruit
color = "black"
color + fruit
Changing a variable (using ASSIGNMENT) just changes the name of an object. It does not change the data inside the object.
This is analogous to a label being removed from one box and placed on a different box.
fruit = "Apple"
snack = fruit
After this both snack and fruit...
This is analogous to two labels being placed on the same box.
most messages return new values
fruit = "banana"
snack = fruit.upcase
"banana" and "BANANA" are two different objects in memory
Most messages do not change the data inside the object.
color.upcase
color
But some messages do change the data!
color.upcase!
color
This can be dangerous so sometimes those messages end with a BANG (exclamation point).
1/12