made find function elemental, updated test cases and documentation accordingly

Author: aman-godara

doc/specs/stdlib_strings.md

@@ -294,7 +294,7 @@ Experimental
 
 #### Class
 
-Pure function
+Elemental function
 
 #### Argument
 
@@ -309,7 +309,7 @@ Pure function
 
 #### Result value
 
-The result is of scalar integer type.
+The result is a scalar of integer type or integer array of rank equal to the highest rank among all dummy arguments.
 
 #### Example
 
@@ -320,12 +320,11 @@ program demo_find
   implicit none
   string_type :: string
 
-  string = "needle in this character-stack"
+  string = "needle in the character-stack"
 
-  print *, find(string, "needle")   ! 1
-  print *, find(string, "a", 3)     ! 28
-  print *, find("qwqwqwq", "qwq", 3, .false.)  ! 0
-  print *, find("qwqwqwq", "qwq", 3, .true.)   ! 5
+  print *, find(string, "needle")                       ! 1
+  print *, find(string, ["a", "c"], [3, 2])             ! [27, 20]
+  print *, find("qwqwqwq", "qwq", 3, [.false., .true.]) ! [0, 5]
 
 end program demo_find
 ```

src/stdlib_strings.f90

@@ -379,7 +379,7 @@ end function slice_char
     !> Returns the starting index of the 'occurrence'th occurrence of substring 'pattern'
     !> in input 'string'
     !> Returns an integer
-    pure function find_string_string(string, pattern, occurrence, consider_overlapping) result(res)
+    elemental function find_string_string(string, pattern, occurrence, consider_overlapping) result(res)
         type(string_type), intent(in) :: string
         type(string_type), intent(in) :: pattern
         integer, intent(in), optional :: occurrence
@@ -393,7 +393,7 @@ end function find_string_string
     !> Returns the starting index of the 'occurrence'th occurrence of substring 'pattern'
     !> in input 'string'
     !> Returns an integer
-    pure function find_string_char(string, pattern, occurrence, consider_overlapping) result(res)
+    elemental function find_string_char(string, pattern, occurrence, consider_overlapping) result(res)
         type(string_type), intent(in) :: string
         character(len=*), intent(in) :: pattern
         integer, intent(in), optional :: occurrence
@@ -407,7 +407,7 @@ end function find_string_char
     !> Returns the starting index of the 'occurrence'th occurrence of substring 'pattern'
     !> in input 'string'
     !> Returns an integer
-    pure function find_char_string(string, pattern, occurrence, consider_overlapping) result(res)
+    elemental function find_char_string(string, pattern, occurrence, consider_overlapping) result(res)
         character(len=*), intent(in) :: string
         type(string_type), intent(in) :: pattern
         integer, intent(in), optional :: occurrence
@@ -421,7 +421,7 @@ end function find_char_string
     !> Returns the starting index of the 'occurrence'th occurrence of substring 'pattern'
     !> in input 'string'
     !> Returns an integer
-    pure function find_char_char(string, pattern, occurrence, consider_overlapping) result(res)
+    elemental function find_char_char(string, pattern, occurrence, consider_overlapping) result(res)
         character(len=*), intent(in) :: string
         character(len=*), intent(in) :: pattern
         integer, intent(in), optional :: occurrence

src/tests/string/test_string_functions.f90

@@ -163,27 +163,34 @@ subroutine test_slice_string
     end subroutine test_slice_string
 
     subroutine test_find
-        type(string_type) :: test_string, test_pattern
-        test_string = "qwqwqwqwqwqwqw"
-        test_pattern = "qwq"
-        call check(find(test_string, test_pattern, 4) == 7, &
-            & 'Find: test_string, test_pattern, 4')
-        call check(find(test_string, test_pattern, 3, .false.) == 9, &
-            & 'Find: test_string, test_pattern, 3')
-        call check(find(test_string, test_pattern, 7) == 0, &
-            & 'Find: test_string, test_pattern, 7')
-        call check(find("qwqwqwqwqwqwqw", test_pattern) == 1, &
-            & 'Find: "qwqwqwqwqwqwqw", test_pattern')
-        call check(find(test_string, "qwq", 2) == 3, &
-            & 'Find: test_string, "qwq", 2')
+        type(string_type) :: test_string_1, test_string_2, test_pattern_1, test_pattern_2
+        test_string_1 = "qwqwqwqwqwqwqw"
+        test_string_2 = "abccbabccbabc"
+        test_pattern_1 = "qwq"
+        test_pattern_2 = "abccbabc"
+
+        call check(all(find([test_string_1, test_string_2], test_pattern_1, 4) == [7, 0]), &
+            & 'Find: [test_string_1, test_string_2], test_pattern_1, 4')
+        call check(all(find(test_string_1, [test_pattern_1, test_pattern_2], 3, .false.) == [9, 0]), &
+            & 'Find: test_string_1, [test_pattern_1, test_pattern_2], 3, .false.')
+        call check(find(test_string_1, test_pattern_1, 7) == 0, &
+            & 'Find: test_string_1, test_pattern_1, 7')
+        call check(all(find([test_string_1, test_string_2, test_string_2], [test_pattern_1, &
+            & test_pattern_2, test_pattern_2], [7, 2, 2], [.true., .false., .true.]) == [0, 0, 6]), &
+            & 'Find: [test_string_1, test_string_2, test_string_2], [test_pattern_1, &
+            & test_pattern_2, test_pattern_2], [7, 2, 2], [.true., .false., .true.]')
+        call check(find("qwqwqwqwqwqwqw", test_pattern_1) == 1, &
+            & 'Find: "qwqwqwqwqwqwqw", test_pattern_1')
+        call check(all(find(test_string_1, ["qwq", "wqw"], 2) == [3, 4]), &
+            & 'Find: test_string_1, ["qwq", "wqw"], 2')
         call check(find("qwqwqwqwqwqwqw", "qwq", 2, .false.) == 5, &
             & 'Find: "qwqwqwqwqwqwqw", "qwq", 2, .false.')
         call check(find("", "") == 0, &
             & 'Find: "", ""')
-        call check(find("", test_pattern) == 0, &
-            & 'Find: "", test_pattern')
-        call check(find(test_string, "") == 0, &
-            & 'Find: test_string, ""')
+        call check(find("", test_pattern_1) == 0, &
+            & 'Find: "", test_pattern_1')
+        call check(find(test_string_1, "") == 0, &
+            & 'Find: test_string_1, ""')
 
     end subroutine test_find