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Diffstat (limited to 'doc/reference/ReferencePart.tex')
| -rw-r--r-- | doc/reference/ReferencePart.tex | 25 |
1 files changed, 13 insertions, 12 deletions
diff --git a/doc/reference/ReferencePart.tex b/doc/reference/ReferencePart.tex index 85902029f6..4c29bd1a74 100644 --- a/doc/reference/ReferencePart.tex +++ b/doc/reference/ReferencePart.tex @@ -762,12 +762,12 @@ transitive relation that satisfies the following conditions. binding of $x$ in $T$ subsuming it, then $T$ conforms to the compound type ~\lstinline@$T_1$ with $\ldots$ with $T_n$ {$R\,$}@. \item If - $T'_i$ conforms to $T_i$ for $i = 1 \commadots n$ and $U$ conforms to $U'$ + $T_i \equiv T'_i$ for $i = 1 \commadots n$ and $U$ conforms to $U'$ then the method type $(T_1 \commadots T_n) U$ conforms to $(T'_1 \commadots T'_n) U'$. \item If, assuming $L'_1 \conforms a_1 \conforms U'_1 \commadots L'_n \conforms a_n \conforms U'_n$ -one has $L_i \conforms L'_i$ and $U'_i \conforms U_i$ +one has $L'_i \equiv L'_i$ and $U_i \equiv U'_i$ for $i = 1 \commadots n$, as well as $T \conforms T'$ then the polymorphic type $[a_1 >: L_1 <: U_1 \commadots a_n >: L_n <: U_n] T$ conforms to the polymorphic type $[a_1 >: L'_1 <: U'_1 \commadots a_n >: L'_n <: U'_n] T'$. @@ -3776,7 +3776,9 @@ inserted by the compiler. A view definition is a normal function definition with one value parameter where the name of the defined function is \code{view}. -\example +\example +The following defines an implicit coercion function from strings to lists of +characters. \begin{lstlisting} def view(xs: String): List[char] = @@ -3784,9 +3786,6 @@ def view(xs: String): List[char] = else xs.charAt(0) :: xs.substring(1); \end{lstlisting} -This defines an implicit coercion function from strings to lists of -characters. - \section{View Application} View applications are inserted implicitly in two situations. @@ -3814,7 +3813,7 @@ Searching a view which is applicable to an expression $e$ of type $T$ is a three-step process. \begin{enumerate} \item -First, the set $\VV$ of available views is determined. $\VV$ is the +First, the set $\AA$ of available views is determined. $\AA$ is the smallest set such that: \begin{enumerate} \item @@ -3849,7 +3848,7 @@ further view conversion of $e$ to the view's formal parameter type. Likewise, a view's result type must conform to a given prototype directly, no second view conversion is allowed. \item -It is an error is the set of applicable views $\BB$ is empty. For +It is an error if the set of applicable views $\BB$ is empty. For non-empty $\BB$, the view method which is most specific (\sref{sec:overloaded-refs}) in $\BB$ is selected. It is an error if no most specific view exists, or if it is not unique. @@ -3920,16 +3919,16 @@ Implicit view parameters of a method or class are then taken as available view methods in its body. \example Consider the following definition of a trait -\code{Comparable} and a view from strings to that trait.. +\code{Comparable} and a view from strings to that trait. \begin{lstlisting} trait Comparable[a] { - def less (x: a): boolean + def less(x: a): boolean } object StringsAreComparable { def view(x: String): Comparable[String] = new Comparable[String] { - def less (y: String) = x.compareTo(y) < 0 + def less(y: String) = x.compareTo(y) < 0 } } \end{lstlisting} @@ -4039,7 +4038,7 @@ allows the definition of conditional views. list element type is also comparable. \begin{lstlisting} -def view[a <% Comparable[a]](x: List[a]): Comparable[List[a]] = +def view[a <% Comparable[a]](xs: List[a]): Comparable[List[a]] = new Comparable[List[a]] { def less (ys: List[a]): boolean = !ys.isEmpty @@ -4057,6 +4056,7 @@ type parameters are translated to implicit \code{view} arguments. In this case, the \code{view} method over lists would receive the \code{view} method over list elements as implicit parameter. +\comment{ This opens up the risk of infinite instantiations because view methods are be passed to themselves as parameters. For instance, one might try to define the following ``magic'' universal converter: @@ -4086,6 +4086,7 @@ argument, either directly or indirectly. On the other hand, contractive view methods may be passed to themselves as arguments. In the examples above this case arises if a list of lists of strings is seen as a \code{Comparable}. +} \chapter{Top-Level Definitions} \label{sec:topdefs} |