Format

A whole template instead of text in pieces: format drops values into a ready caption

easyYou need: The text buffer, Print Flush

print assembles a caption in pieces, and on a long phrase that becomes awkward: the text is split across lines of the program, and what it will finally look like exists only in your head.

format works the other way round: first the whole template goes into the buffer, then values are substituted into it.

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Sensor0

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 in

Print1

Format2

Format3

Print Flush4

Wait5

@counter0number

coppernullnull

textBuffer—string

Press “run”. Under the message block you get copper 120 of 300: the template copper {0} of {1} went into the buffer first, and two formats replaced its placeholders in turn.

A placeholder is exactly three characters

A placeholder looks like {0}: an opening brace, a digit from 0 to 9, a closing brace. No spaces, no numbers above nine — such a thing simply does not count as a placeholder, and format will not see it.

Silent failure

If there is no suitable placeholder in the buffer, format does nothing — silently. No error, no appending at the end. The value simply disappears, and the caption keeps a template with an unfilled placeholder.

The most common cause: format standing before the print with the template. The buffer is empty at that moment, and there is nowhere to substitute into.

The smallest number wins, not the first placeholder

This rule surprises people. format searches the buffer for the placeholder with the smallest number, not the one that comes first.

For the template {1} and {0} the first format substitutes at the end — where {0} is. The order of substitutions is set by the numbers, not by their position in the string.

Note

Hence a simple rule: number the placeholders in the order you intend to fill them, not in the order they stand in the text. Then the phrase can be written the way it reads naturally — “{1} left out of {0}” — and still be filled in limit first, remainder second.

A placeholder disappears once filled

A replaced placeholder is gone from the buffer, so the next format finds the next one by number. Two values cannot go into one placeholder, and an extra format with none free does nothing.

What is in the buffer	format 120 gives
copper {0}	copper 120
{1} and {0}	{1} and 120
copper 0	copper 0 — no placeholder, the value is lost
empty	empty — nowhere to substitute

Values turn into text by the same rules as with print: a whole number prints without a fraction, a building as its block’s name, emptiness as the word null. That is the lesson “What prints as what”.

Remember

• format substitutes a value into the {N} placeholder inside the buffer.
• Template first, substitutions after — otherwise there is nowhere to substitute.
• The placeholder with the smallest number is taken, not the first in the string.
• A placeholder disappears once filled, and an extra format silently does nothing.

Task

Change the template to left {1} of {0} and run it: you get left 300 of 120 — the numbers decide what goes where, and the values swapped places even though the format lines stayed the same.

Then remove {1} from the template: the second format is left without a placeholder and keeps quiet, and the caption stays copper 120 of.