## digitalmars.D.learn - Check if give an array is equal to first elements in another array

```Is there one function in the Phobos library to check if give an
array is equal to first elements in another array? e.g, f(a, b)
the entire b array must match to first elements in a and then
return true otherwise false, ie:

a[0 .. b.length] == b

probably there's no such a function (but I wouldn't find bad if
there was) in the D's library so what's a good name (that'a
descriptive) to such a function?

btw, what it solves is:

if(a.length >= b1.length && a[0 .. b1.length] == b1) { ... }
if(a.length >= b2.length && a[0 .. b2.length] == b2) { ... }

since if bx.length < a.length is valid I can't remove all the
a.length >= bx.length checks otherwise I can have a range
violation error
```
Oct 15 2014
```On Thursday, 16 October 2014 at 04:35:13 UTC, MachineCode wrote:
Is there one function in the Phobos library to check if give an
array is equal to first elements in another array?

auto n = min(a.length, b.length);
if (a[0..n] == b[0..n]) ...
```
Oct 15 2014    =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
```On 10/15/2014 09:35 PM, MachineCode wrote:
Is there one function in the Phobos library to check if give an array is
equal to first elements in another array? e.g, f(a, b) the entire b
array must match to first elements in a and then return true otherwise
false, ie:

a[0 .. b.length] == b

probably there's no such a function (but I wouldn't find bad if there
was) in the D's library so what's a good name (that'a descriptive) to
such a function?

btw, what it solves is:

if(a.length >= b1.length && a[0 .. b1.length] == b1) { ... }
if(a.length >= b2.length && a[0 .. b2.length] == b2) { ... }

since if bx.length < a.length is valid I can't remove all the a.length
>= bx.length checks otherwise I can have a range violation error

import std.algorithm;

void main()
{
auto a = [ 1, 42, 100, 7 ];
auto b = [ 1, 42 ];
assert(a.startsWith(b));
}

Ali
```
Oct 15 2014