A turner is a one-time glider reflector, or in other words a single-glider seed. The term "turner" is seldom used in relation to spaceships other than gliders. A reusable turner would instead be called a reflector.
One-time turners may be 90-degree or 180-degree, or they may be 0-degree with the output in the same direction as the input. Shown on the top row below are the four 90-degree turner reactions that use common small ash objects: boat, eater1, long boat, and toad.
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Of the reactions on the first row, the glider output is the same parity for all but the longboat. The three still lifes are all colour-changing, but the toad happens to be a colour-preserving turner. Many small one-time turner constellations have also been catalogued.Michael Simkin (November 27, 2014). "Splitters with common SL". Retrieved on January 28, 2018. The two-block turner directly below the toad is also colour-changing, but has the opposite parity. In the southwest corner above are two of the simplest 180-degree turners. The Blockic turner is colour-preserving. The long boat is again colour-changing; this is somewhat counterintuitive as the output glider is on exactly the same lane as the input glider, but gliders traveling in opposite directions on the same lane are always opposite colours.
A one-time turner reaction can be used as part of a glider injection mechanism, or as a switching mechanism for a signal. If a previous reaction has created the sacrificial bait object, then a later glider is turned onto a new path. Otherwise it passes through the area unaffected. This is one way to create simple switching systems or logic circuits such as the demultiplexer.