Does a Pine Script switch Need a Default Branch?

Default syntax and the two switch forms

Use switch mode to match a value, or switch on its own line to evaluate boolean conditions in order. Only the first matching branch executes. Its final expression is the result, so break is unnecessary. The complete v6 script below selects a price and then a color. With mode set to Off, the default returns float(na), intentionally hiding the plot.

//@version=6
indicator("Switch default syntax", overlay=true)

mode = input.string("Close", "Source", options=["Close", "Open", "Off"])
price = switch mode
    "Close" => close
    "Open" => open
    => float(na)

lineColor = switch
    close > open => color.green
    close < open => color.red
    => color.gray

plot(price, "Selected source", color=lineColor)

No matching branch: v5 and v6 behavior

The version annotation matters when a switch has no default. Numeric na is still a missing value in v6, but bool no longer has a third state. This v5 example leaves Off unmatched and displays its boolean na state as -1. The table distinguishes an ordinary omitted fallback from the v6 unique-type restriction.

//@version=5
indicator("Unmatched boolean in v5")
mode = input.string("Off", "Mode", options=["On", "Off"])
bool selected = switch mode
    "On" => true

state = na(selected) ? -1 : selected ? 1 : 0
plot(state, "1 = true, 0 = false, -1 = na")

Migrating an unmatched boolean to v6

Do not carry na(selected), nz(selected), or fixnan(selected) into v6 when selected is bool. Those functions no longer accept boolean arguments. Here Off becomes false, plotted as 0. If Off must mean unknown rather than false, represent that state explicitly instead of relying on a boolean na.

//@version=6
indicator("Unmatched boolean in v6")
mode = input.string("Off", "Mode", options=["On", "Off"])
bool selected = switch mode
    "On" => true

plot(selected ? 1 : 0, "1 = true, 0 = false")

The v6 case where a default really is required

plot.style_line and plot.style_columns have the unique plot_style type. In v6, a switch that returns this type needs a default, even when its cases cover the input options. The example supplies plot.style_line as the final branch. Remove that branch to reproduce the missing-default compilation problem; leave it in the working script.

//@version=6
indicator("Switch plot style fallback")
mode = input.string("Line", "Style", options=["Line", "Columns"])
selectedStyle = switch mode
    "Line" => plot.style_line
    "Columns" => plot.style_columns
    => plot.style_line

plot(close, "Close", style=selectedStyle)

Return types, multiline blocks, and tuples

When you assign a switch result, branch results must have compatible types. Numeric int values can widen to float; a string cannot become a price. A branch may declare local variables before returning its final expression. Tuples can contain different types, but every branch must return the same number of items with compatible types in corresponding positions. The example returns a float and a color together.

• A numeric branch ending in "Off" is a type mismatch. Use float(na) for a missing numeric value, or keep the status text in a separate variable.
• Write [value, tint] = switch to declare tuple results. Do not put type keywords inside the tuple declaration.
• Tuple items share a qualifier. Combining a series price and an integer length can make the length series int, which ta.ema() does not accept.

//@version=6
indicator("Switch tuple return", overlay=true)
mode = input.string("Midpoint", "Source", options=["Midpoint", "Close", "Off"])

[value, tint] = switch mode
    "Midpoint" =>
        float midpoint = (high + low) / 2.0
        [midpoint, color.blue]
    "Close" => [close, color.orange]
    => [float(na), color.gray]

plot(value, "Selected value", color=tint)

Scope: use := to update an existing variable

Each branch is a local scope. Declaring a same-named variable with = inside it shadows the outer variable; it does not update that variable. Use := for reassignment. Ordinary declarations run whenever their scope executes; var initializes on the first execution of its scope. Here direction persists with var, and the fallback resets it to zero on a doji bar. Without that fallback, a doji would preserve its previous value.

//@version=6
indicator("Switch reassignment")
var int direction = 0

switch
    close > open => direction := 1
    close < open => direction := -1
    => direction := 0

plot(direction, "Bar direction")

Diagnose the error before adding a fallback

These are diagnostic categories, not guaranteed compiler message wording. Fix the constraint named by the error, then compile the entire script. Syntax validation does not check whether a chosen fallback matches your trading rules. The examples on this page demonstrate language behavior, not a trading strategy.