How to group values in your own type

When several values belong together, such as a price and the bar it was seen on, declare a type and keep one instance of it. The instance holds the values; you read a field with a dot and change it with :=.

//@lipi=2
indicator("Highest high so far", overlay=true)
type Peak {
    float price
    int barIndex = 0
}
static Peak top = Peak.new(high, bar_index)
if high > top.price {
    top.price := high
    top.barIndex := bar_index
}
plot(top.price, title="Highest high")
if barstate.islast {
    label.new(top.barIndex, top.price, "Peak " + str.tostring(top.price), style=label.style_label_down)
}

type Peak { ... } is declared at the top level, one field per line, before it is used. A field may have a default that is a plain value (a number, a string, true, false, a color constant, na or a built-in variable such as close).
Peak.new(high, bar_index) creates an instance; arguments follow the field order or may be named. A field left out takes its default, or na when it has none.
static creates the instance once, on the first bar, and keeps it from bar to bar. A field changed with := keeps its new value on the next bar.

The mistake to avoid

Changing a field with =. A field is changed with :=, like any existing variable. The compiler says: To assign a new value to an object’s property, use := instead of =.

//@lipi=2
indicator("Field assigned with =", overlay=true)
type Peak {
    float price
}
static Peak top = Peak.new(high)
top.price = high
plot(top.price)

An instance is shared, not copied: b = top gives a second name for the same object. Use top.copy() for an independent one. See Custom types and enums.

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Reference

How to group values in your own type

The mistake to avoid

​The mistake to avoid

The mistake to avoid