<commit_before>#ifndef STAN_MATH_PRIM_FUNCTOR_APPLY_SCALAR_UNARY_HPP
#define STAN_MATH_PRIM_FUNCTOR_APPLY_SCALAR_UNARY_HPP

#include <stan/math/prim/fun/Eigen.hpp>
#include <stan/math/prim/meta/is_eigen.hpp>
#include <stan/math/prim/meta/is_vector.hpp>
#include <stan/math/prim/meta/is_vector_like.hpp>
#include <utility>
#include <vector>

namespace stan {
namespace math {

/**
 * Base template class for vectorization of unary scalar functions
 * defined by a template class <code>F</code> to a scalar,
 * standard library vector, or Eigen dense matrix expression
 * template.
 *
 * <p>Specializations of this base define applications to scalars
 * (primitive or autodiff in the corresponding autodiff library
 * directories) or to standard library vectors of vectorizable
 * types (primitives, Eigen dense matrix expressions, or further
 * standard vectors).
 *
 * <p>Each specialization must define the typedef
 * <code>return_t</code> for the vectorized return type and the
 * function <code>apply</code> which defines the vectorization or<commit_msg>added missing header<commit_after>#ifndef STAN_MATH_PRIM_FUNCTOR_APPLY_SCALAR_UNARY_HPP
#define STAN_MATH_PRIM_FUNCTOR_APPLY_SCALAR_UNARY_HPP

#include <stan/math/prim/fun/Eigen.hpp>
#include <stan/math/prim/meta/is_eigen.hpp>
#include <stan/math/prim/meta/is_vector.hpp>
#include <stan/math/prim/meta/is_vector_like.hpp>
#include <stan/math/prim/meta/plain_type.hpp>
#include <utility>
#include <vector>

namespace stan {
namespace math {

/**
 * Base template class for vectorization of unary scalar functions
 * defined by a template class <code>F</code> to a scalar,
 * standard library vector, or Eigen dense matrix expression
 * template.
 *
 * <p>Specializations of this base define applications to scalars
 * (primitive or autodiff in the corresponding autodiff library
 * directories) or to standard library vectors of vectorizable
 * types (primitives, Eigen dense matrix expressions, or further
 * standard vectors).
 *
 * <p>Each specialization must define the typedef
 * <code>return_t</code> for the vectorized return type and the
 * function <code>apply</code> which defines the vectorization or
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