Number, object and text

A variable holds either a number or an object — and what you can do with it follows from that

easy

An mlog variable holds either a number or an object. Everything that is not a number is an object: a string, an item, a block, a unit, a team. Emptiness, null, is a kind of object all its own, and it gets a lesson of its own.

steptick 0

Set0

=

Set1

=

Set2

=

Set3

=

@counter0number

numbernullnull

textnullnull

itemnullnull

unsetnullnull

To the right of the value the table shows the kind: number, string, content, null. It is the same column the “Variables” window shows in the game itself, in the same colours.

The kind arrives together with the value

A variable does not hold a kind by itself. Write a number into it and it is a number; write @copper and it is an object. The same variable is both at different points in a program’s life, and nobody complains.

There is nowhere and no need to declare a kind in advance: mlog has neither types in a declaration nor a check on assignment. The only place the kind is visible is the variables table.

An object in arithmetic is a one

Numbers count as numbers. But when an object lands in arithmetic, the game does not work out what it is:

• op add two @copper 1 gives 2, because copper as a number is a one;
• the same happens with any building, unit or string;
• and only null gives zero — that is the next lesson.

The rule is simple: any object in a numeric context equals one, emptiness equals zero. This is not a “type conversion” but a rule, and there is no other way to get a number out of an object.

A string is not text for arithmetic

"copper" is a string: print, format and comparisons work with it, arithmetic does not. You can add a string to a number, only the result will not be what you expect: the string goes into the sum as an object, that is, as a one.

Silent failure

Hence a common beginner’s mistake: comparing a block’s type with a string. sensor kind block1 @type puts a type object into the variable, not the word “container”, and equal kind "container" will never be true. It has to be compared with the constant @container.

Remember

• A variable holds either a number or an object; the kind arrives with the value.
• A string, an item, a block, a unit and a team are all objects.
• In arithmetic any object equals one, and null equals zero.
• A block’s type is an object, not a string: compare it with the constant.

Task

Add an Operation line with the plus, choose +, put check on the left and add item and 1 on the right — you get a two.

Then replace item with text: a two again. Copper, a string and any other object are indistinguishable in arithmetic — all of them are a one.