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view: add slicing operation, stolen from python

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This commit is contained in:
Danny Robson 2018-01-29 17:17:28 +11:00
parent f9a202877a
commit 32a4aa23e5
2 changed files with 52 additions and 12 deletions
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46
test/view.cpp
View File

@ -15,19 +15,21 @@ main (int, char**)
"character array view does not include trailing null"
);
const std::string s = "this is a test string";
const std::string t = "not the same string";
tap.expect_eq (s, util::make_view(s), "string/view equality");
tap.expect_neq (s, util::make_view(t), "string/view inequality");
tap.expect_eq (s.data (), util::make_view (s), "c-str/view equality");
tap.expect_eq (
s,
util::view<const char*> (&*s.cbegin (), &*s.cend ()),
"string/pointer-view equality");
{
// comparator tests
const std::string s = "this is a test string";
const std::string t = "not the same string";
tap.expect_eq (s, util::make_view(s), "string/view equality");
tap.expect_neq (s, util::make_view(t), "string/view inequality");
tap.expect_eq (s.data (), util::make_view (s), "c-str/view equality");
tap.expect_eq (
s,
util::view<const char*> (&*s.cbegin (), &*s.cend ()),
"string/pointer-view equality");
}
// comparator tests
{
static const struct {
util::view<const char*> a;
util::view<const char*> b;
@ -48,5 +50,25 @@ main (int, char**)
}), "comparator less-than");
};
// slicing
{
static const struct {
const char *init;
const char *result;
int a;
int b;
const char *message;
} TESTS[] = {
{ "01234567", "01234567", 0, 8, "identity, +ve +ve" },
{ "01234567", "01234567", 0, -1, "identity, +ve -ve" },
{ "01234567", "", -1, -1, "empty, -ve -ve" },
{ "01234567", "45", 4, -3, "centre, +ve -ve" },
};
for (const auto &t: TESTS) {
tap.expect_eq (util::view { t.init }.slice (t.a, t.b), t.result, "slice; %s", t.message);
}
}
return tap.status ();
}

18
view.hpp
View File

@ -308,6 +308,24 @@ namespace util {
}
//---------------------------------------------------------------------
// slices a view using python indexing semantics. ie,
// "abc".slice(0, 3) == "abc"
// "abc".slice(0, -1) == "abc"
// "abc".slice(0, -2) == "ab"
constexpr auto
slice (int a, int b)
{
auto first = m_begin;
auto last = m_begin;
std::advance (first, a < 0 ? size () + a + 1 : a);
std::advance (last, b < 0 ? size () + b + 1 : b);
return util::view { first, last };
}
//---------------------------------------------------------------------
constexpr auto
consume (int count) const