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Function std.exception.handle

Handle exceptions thrown from range primitives.

auto handle(E, RangePrimitive primitivesToHandle, alias handler, Range) (
  Range input
if (isInputRange!Range);

Use the RangePrimitive enum to specify which primitives to handle. Multiple range primitives can be handled at once by using the OR operator or the pseudo-primitives RangePrimitive.access and RangePrimitive.pop. All handled primitives must have return types or values compatible with the user-supplied handler.


E The type of Throwable to handle.
primitivesToHandle Set of range primitives to handle.
handler The callable that is called when a handled primitive throws a Throwable of type E. The handler must accept arguments of the form E, ref IRange and its return value is used as the primitive's return value whenever E is thrown. For opIndex, the handler can optionally recieve a third argument; the index that caused the exception.
input The range to handle.


A wrapper struct that preserves the range interface of input.


Infinite ranges with slicing support must return an instance of std.range.Take when sliced with a specific lower and upper bound (see hasSlicing); handle deals with this by takeing 0 from the return value of the handler function and returning that when an exception is caught.


import std.algorithm.comparison : equal;
import std.algorithm.iteration : map, splitter;
import std.conv : to, ConvException;

auto s = "12,1337z32,54,2,7,9,1z,6,8";

// The next line composition will throw when iterated
// as some elements of the input do not convert to integer
auto r = s.splitter(',').map!(a => to!int(a));

// Substitute 0 for cases of ConvException
auto h = r.handle!(ConvException, RangePrimitive.front, (e, r) => 0);
assert(h.equal([12, 0, 54, 2, 7, 9, 0, 6, 8]));


import std.algorithm.comparison : equal;
import std.range : retro;
import std.utf : UTFException;

auto str = "hello\xFFworld"; // 0xFF is an invalid UTF-8 code unit

auto handled = str.handle!(UTFException, RangePrimitive.access,
        (e, r) => ' '); // Replace invalid code points with spaces

assert(handled.equal("hello world")); // `front` is handled,
assert(handled.retro.equal("dlrow olleh")); // as well as `back`


Andrei Alexandrescu and Jonathan M Davis


Boost License 1.0