UltiSnips at the present day is more than snippet engine. It's more like constructor, where you can implement some complex features without prior feature implementation in the snippet by itself.
One of that features is dynamic tabstop generation.
Consider case, where you want set of snippets for inserting latex rows of various lengths. No-brainer solution is just implement snippet for every row length you're possible will want, like this:
snippet tr9 "LaTeX table row of length nine"
$1 & $2 & $3 & $4 & $5 & $6 & $7 & $8 & $9
endsnippet
But soon it becomes a burden to maintain that kind of snippets.
Gladly, tabstops can be generated by using anonymous snippet expansion:
global !p
def create_row_placeholders(snip):
# retrieving single line from current string and treat it like tabstops
# count
placeholders_amount = int(snip.buffer[snip.line].strip())
# erase current line
snip.buffer[snip.line] = ''
# create anonymous snippet with expected content and number of tabstops
anon_snippet_body = ' & '.join(['$' + str(i+1)
for i in range(placeholders_amount)])
# expand anonymous snippet
snip.expand_anon(anon_snippet_body)
endglobal
post_jump "create_row_placeholders(snip)"
snippet "tr(\d+)" "latex table row variable" br
`!p snip.rv = match.group(1)`
endsnippet
Snippet is declared via regular expression and will expand to any required number of fields in row.
Now, for a more robust tabstop generation, to create placeholders within multiple lines:
global !p
def create_matrix_placeholders(snip):
# Create anonymous snippet body
anon_snippet_body = ""
# Get start and end line number of expanded snippet
start = snip.snippet_start[0]
end = snip.snippet_end[0]
# Append current line into anonymous snippet
for i in range(start, end + 1):
anon_snippet_body += snip.buffer[i]
anon_snippet_body += "" if i == end else "\n"
# Delete expanded snippet line till second to last line
for i in range(start, end):
del snip.buffer[start]
# Empty last expanded snippet line while preserving the line
snip.buffer[start] = ''
# Expand anonymous snippet
snip.expand_anon(anon_snippet_body)
def create_matrix(cols, rows, sep, start, end):
res = ""
placeholder = 1
for _ in range(0, int(rows)):
res += start + f"${placeholder} "
placeholder += 1
for _ in range(0, int(cols) - 1):
res += sep + f" ${placeholder} "
placeholder += 1
res += end
return res[:-1]
endglobal
post_jump "create_matrix_placeholders(snip)"
snippet 'arr(\d+),(\d+)' "LaTeX array" br
\begin{array}{`!p
orient = ""
for _ in range(0, int(match.group(1))): orient += "l"
snip.rv = orient`}
`!p
snip.rv = create_matrix(match.group(1), match.group(2), "&", "\t", "\\\\\\\\\n")
`$0
\end{array}
endsnippet