A one-time turner consists of a constellation or other pattern that can be hit by a glider to produce another glider travelling in a different direction, destroying the turner in the process. This contrasts with one-time converters, which produce an output different from the input. In a dirty turner the reaction leaves behind one or more ash objects different from the original constellation.
One-time turners are an important component for slow salvo synthesis, where they are frequently used to change the direction from which a trigger glider will hit the reaction site. They may be 90-degree or 180-degree, or they may be 0-degree with the output in the same direction as the input (in which case they may instead be referred to as one-time rephasers or shifters). Shown on the top row below are the four 90-degree turner reactions that use common small ash objects: boat, eater 1, long boat, and toad.
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Of the reactions on the first row, the glider output parity is even for the boat, eater and toad, and odd for the long boat and the Blockic 90-degree turner at the far right. The three singleton still lifes are all colour-changing, but the toad and Blockic 90-degree turner are colour-preserving.
Three of the simplest 180-degree turners are shown in the second row. The blockic 180-degree turner is colour-preserving. The long boat and long ship are 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 always have opposite colours. At the right end of the second row is an aircraft carrier serving as a colour-changing "0-degree turner".
The third row shows two turners that are unusually effective one-time inserters, placing gliders close to existing gliders. The pond and long boat turner can place a 90-degree output glider directly behind an existing glider at the minimum separation of 14 ticks; the beehive and boat turner can place a 180-degree output glider directly in front of an existing glider, again at the minimum possible separation. Many other turner-based glider injection mechanisms are available, depending on the required clearance around the inserted glider.
The right side of the third row shows a long long boat and block to split one glider into three gliders. Three-glider outputs are very rare compared to the 1G-to-2G splitters shown on the fourth row. The first two are modifications of singleton turners directly above them in the table; in each case a second still life is added that uses a transient spark to produce an additional glider. The loaf and block has the output gliders on different parities and different colours, and a passing glider needs to be at least 3 lanes away, whereas the highway-robbing boat and block has the output gliders on the same parity and same colour.
Many small one-time turner constellations have also been catalogued, which can be found at external link below.
A one-time turner reaction can be used 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.