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to construct a coerce method.
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to construct a coerce method.
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In the usual case that the subclass contains the superclass (i.e., has
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In the usual case that the subclass contains the superclass (i.e., has
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all its slots), the method is constructed either by extracting or
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all its slots), the method is constructed either by extracting or
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replacing the inherited slots.
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replacing the inherited slots.
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Non-simple extensions (the result of a call to \code{\link{setIs}})
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Non-simple extensions (the result of a call to \code{\link{setIs}})
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will usually contain explicit methods, though possibly not for replacement.
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will usually contain explicit methods, though possibly not for replacement.
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If no subclass/superclass relationship provides a method, \code{as}
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If no subclass/superclass relationship provides a method, \code{as}
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looks for an inherited method, but applying, inheritance for the argument \code{from} only, not for
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looks for an inherited method, but applying, inheritance for the argument \code{from} only, not for
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the argument \code{to} (if you think about it, you'll probably agree
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the argument \code{to} (if you think about it, you'll probably agree
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that you wouldn't want the result to be from some class other than the
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that you wouldn't want the result to be from some class other than the
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\code{Class} specified). Thus,
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\code{Class} specified). Thus,
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\code{selectMethod("coerce", sig, useInherited= c(from=TRUE, to= FALSE))}
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\code{selectMethod("coerce", sig, useInherited= c(from=TRUE, to= FALSE))}
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replicates the method selection used by \code{as()}.
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replicates the method selection used by \code{as()}.
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In nearly all cases the method found in this way will be cached in the
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In nearly all cases the method found in this way will be cached in the
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table of coerce methods (the exception being subclass relationships with a test, which
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table of coerce methods (the exception being subclass relationships with a test, which
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are legal but discouraged).
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are legal but discouraged).
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So the detailed calculations should be done only on the first
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So the detailed calculations should be done only on the first
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occurrence of a coerce from \code{class(object)} to \code{Class}.
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occurrence of a coerce from \code{class(object)} to \code{Class}.
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